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THREE

TREATISES.

THE BRAIN, THE EYE,

AND

THE EAR.

I L L U S T R ATED BY TABLES.

ALEXANDER MONRO, M. D.

— o <

PROFESSOR OF MEDICINE, ANATOMY, AND SURGERY, IN THE UNIVERSITY.
OF EDINBURGH } FELLOW OF THE ROYAL COLLEGE OF PHYSICIANS,
AND OF THE ROYAL SOCIETY, OF EDINBURGH ; AND FELLOW
OF THE ROYAL ACADEMY OF SURGERY OF PARIS.

EDINBURGH :

PRINTED FOR BELL & BRADFUTE ;

AND FOR G. G. & J. ROBINSON, AND J. JOHNSON)
LONDON.

M.DCC.SCVII. •

\ '

OBSERVATIONS

ON THE

COMMUNICATION

OF THE

VENTRICLES OF THE BRAIN

WITH EACH OTHER;

AND ON THE

INTERNAL

HYDROCEPHALUS.

ALEXANDER MONRO, M. D.

PROFESSOR OF MEDICINE, ANATOMY, AND SURGERY,
IN THE UNIVERSITY OF EDINBURGH,

EDINBURGH:

PRINTED BY ADAM NEILL AND COMPANY,

1797*

'GENERAL

TABLE OF CONTENTS*

TREATISE I.

ON THE BRAIN,

Page 9

— II.

ON THE EYE,

— — HR

ON THE EAR,

*77

Digitized by the Internet Archive

in 2015

https://archive.org/details/b21516807

A Table of the Contents of Treatife I.

CHAP. i.

OF the Communication of the Ventricles of the Brain
with each other, in Man and Quadrupeds,
Explanation of the Tables,

CHAP. II.

Of the Situation of the Water in the Internal Hydro-
cephalus, -

CHAP. III.

Of Changes produced in the Texture of the Brain and
Cerebellum, in confequence of Hydrocephalus Inter-
nus, - -

CHAP. IV.

An Attempt to prove, that the Changes in the Texture
of the Brain and Cerebellum, in confequence of In-
ternal Hydrocephalus, are produced by the Abforbent
Veflels, -

Page

CHAP.

Vlll

CONTENTS OF TREATISE I.

CHAP, V.

Circumftances enumerated, which prove, that the Solid,

Parts compoling other Organs of our Body are Ab-

Pagc

forbed, ------ 47

CHAP. VI.

At what Time the Circumftances enumerated in the laffc
Chapter were firlh taught by the Author, - 55

CHAP. VII.

Of the Cure of Internal Hydrocephalus by Medicines, 61

CHAP. VIII.

Of the Cure of Internal Hydrocephalus by Chirurgical
Operation, - ^ - - - - 67

TREATISE

FIRST:

OF THE BRAIN.

CHAP. L

Of the Communication of the Ventricles of
the Brain with each other, in Man and

QO far back as the year 1753, foon after I began the flu-
dy of Anatomy, I difcoverecl, that the Lateral Ventricles
of the Human Brain communicated with each other, and, at
the fame place, with the Middle or Third Ventricle of the
Brain: And, as a paffage from the Third Ventricle to the
Fourth is univerfally known, it followed, that what are called
the Four Ventricles of the Brain, are in reality different parts
of one cavity.

OF THE COMMUNICATION BETWEEN

In confirmation of this, I afterwards obferved, in the bodies
of fifteen different perfons who had died of Internal Hydro-
cephalus, that the water was lodged in all the Ventricles ;
that by one pundture it was difcliarged from all of them ;
and that the paffages by which I had found the Ventricles
communicated, were dilated in the fame proportion as the
other parts of the Ventricles.

If, therefore, there has been no miflake in the obfervations
of thofe who tell us, that in Hydrocephalus they have found
the water confined to One of the Lateral Ventricles, or dis-
charged by a pundture from One Ventricle, without emptying
the others ; there muft have been, previous to the Dropfy, fome
degree of inflammation, or other difeafe, in that part of the
brain, which had occafioned an obliteration of their natural
c ommiini cations.

I found likewife, that there is no paflage, fuch as Dr Hal-
ler, and other authors, fuppofed, (See Haller, El. Phyf. L. x.
S. 2. § 6. p. 77. and S. 3. § 7. p. 87.) leading from the Ca-
vity of the Fourth Ventricle into the Cavity, as it is called,
of the Spinal Marrow, or, between the Dura and Pia Mater
of the Spinal Marrow.

THE VENTRICLES OF THE BRAIN.

la the year 1764, I read a paper on that fubjed to the Phi-
lofophical Society of Edinburgh : And, in 1783, when I pu-

blifhed my book upon the Nervous Syllem, I gave fuch a
full defcription of the Communications of the Ventricles of
the Brain, illuflrated by figures, that I did not fuppofe any
perfon, who pretended to anatomical knowledge, could find
difficulty in tracing by diffedion all I had defcribed.

To my very great furprife, however, I have been informed,
that feveral Teachers of Anatomy in London have told their
Pupils, that they had looked for fuch paflages in vain ; and
therefore ventured to deny their exigence.

But I cannot admit their inference : becaufe, in the firfl
place, I have found, on repeating my diffedions in private,
that the defcriptions I publifhed in 1783 are fo correct, that
I obferve nothing material to add to, or to alter in them.

In the next place, fince I heard of thofe doubts as to the
fads I had defcribed, I have demonflrated, annually, to all
the Students of Anatomy who have done me the honour of
attending my Ledures, every thing I had mentioned. Par-
ticularly, laft winter, after I had demonflrated thefe parts in
one fubjed, I diffeded another, of which my affiflant Mr

B 2 Fyfe

OF THE COMMUNICATION BETWEEN

Fyfe made a very accurate drawing; which I fhewed to all
the Students, who compared it with the fubjed.

But, that no doubt might remain with the molt fceptical
perfon, I have, this fummer, repeated the diffedion of a re-
cent fubjed ; of which, likewife, Mr Fyfe made a very ac-
curate drawing, that correfponds exadly with his former fi-
gure.

I then afked the favour of all my Colleagues of the Me-
dical Faculty, to wit, Dr Black, Dr Home, Dr Ruther-
ford, Dr Gregory, and Dr Duncan, to compare the
Drawings with the parts difieded ; which they were fo ob-
liging as to do : And I fubjoin their Declaration.

After they had fmifhed their comparifon of the Drawing
marked Table Fir ft, with the diffeded Brain ; I held the
end of a blow-pipe at the diftance of half an inch from
the hole by which the Lateral Ventricles communicate; and,
on my blowing moderately, I fhewed them, that the air
palled from the Right into the Left Lateral Ventricle.

I then opened the Left Lateral Ventricle, and pointed out
to them the hole by which the air had palled.

THE VENTRICLES OF THE BRAIN.

I afterwards made a Call in Paris Plafter of the Parts
reprefented in the Firft Figure : And this caft, which I

preferve, correfponds exa&ly with the Drawing and Engra-
ving.

DECLARATION by the Professors of the Facul-
ty of Physic in the Univerbty of Edinburgh.

“ We whole names are fubfcribed hereby declare, That on
the 13th day of June 1794, Dr Monro demonftrated to
“ us, in the Anatomical Theatre, the Human Brain cut per-
“ pendicularly at the right tide of its Septum Lucidum ; and,
“ along with it, a Drawing of it, marked Table Firft, juft
“ finilhed by Mr Fyfe : That we examined and compared

eC thefe accurately together, and found them to correfpond
“ in all refpecis ; particularly, we faw diftinctly a hole or
“ paftage by which the Lateral Ventricles communicate with
each other, and with the Third Ventricle.

OF THE COMMUNICATION BETWEEN

“ After this, Dr Monro placed the fmall end of a com-
n moil blow-pipe about half an inch from this hole or paf-
“ fage ; and, on his blowing air gently, we faw it pafs •
u through the above-mentioned hole or paflage into the Left
“ Lateral Ventricle.

11 He afterwards fhewed us the Left Lateral Ventricle

laid open, and a Drawing of its parts by Mr Fyfe,
u marked Table Second ; and particularly, we faw the left
“ hde of the paffage which makes the communication be-
ei tween the Ventricles.

» "

u Fie has, lince that time, fhewed us a Caft in Paris

“ Plafter of the Parts reprefented in Table Firft, which we
cl find to correfpond exactly with the Drawing and Engra-
a ving.

“ We therefore entertain no doubt of the exiftence of the
“ Communication of the Lateral Ventricles of the Brain
“ with each other, and with the Third Ventricle, defcribed
“ by Dr Monro in the Work he publifhed on the Nervous

“ Syftem in 1783 ; and particularly, we attefi; the accuracy

“ of the Figures and Defcription of thefe Parts which he

“ fhewed

THE VENTRICLES OF THE BRAIN. 15

“ fhewed us, and which he propofes to prefent to the Royal
a Society of Edinburgh for publication.

“ Joseph Black,.

“ Francis Home.

“ James Gregory.

“ D, Rutherford.

“ Andrew Duncan.”

My very ingenious and intelligent Colleague Dr Ruther»
ford, who, as one of the ordinary Phylicians of the Royal
Infirmary, as well as one of the Clinical Lecturers there,
has had frequent opportunity of examining this fubjedl, has
very obligingly favoured me with his farther atteftation con-
cerning it in the following Letter,

FQ£

OF THE COMMUNICATION BETWEEN

For Dr Monro.

“ Dear Sir,

“ I am very much pleafed with your Drawings and De-
** feription of the Communication of the Lateral Ventricles
“ with each other, and with the other Ventricles of the
“ Brain. The Firft Figure is particularly excellent ; and
“ mud; certainly, I fliould think, remove all doubts refpeding
11 the reality of thefe paflages. It feems indeed very ftrange,
“ that fo many celebrated Anatomifls fliould have mifled the
“ Communication betwixt the Lateral Ventricles , as it is fo
“ eafily difeovered, and as it is generally fo very confpicuous
“ when the Ventricles are dift ended by water preternaturally
“ accumulated in them. Frequently, when examining the
il Hate of the Brain in perfons who had died in the Royal In-
“ firmary, I have taken the opportunity of pointing out this
u Communication to the Young Gentlemen who were prefent
“ at the dlfleflion ; and have fatisfied fome, that it was al-
u ways to be found, who had been taught that no fuch Com-
“ munication exifled. I particularly recoiled; one inftance
££ of this. A very ingenious and well-informed American,

“ Mr

THE VENTRICLES OF THE BRAIN,

“ Mr Philip Physick, who got his degree of M. D. at our
“ Univerfity two years ago, and who had previoufly ap-
“ plied clofely to the ftudy of Anatomy, and made great
“ proficiency in it, under fome of the molt eminent Teach-
“ ers in London, requefted me to fhew him the Communica-
“ tion betwixt the Lateral Ventricles, as he had never been
“ able to perceive it. I did fo ; and he viewed it then, for
“ the fir ft time, with much fiirprife. It is not poflible to mif-
t( take it for an accidental laceration, the edge is fo ex-
“ tremely neat, fmooth and regular. No doubt, it is more
“ diftindt in fome inftances than in others ; and it may be,
“ that, if the Ventricles were only juft moift or without any
“ fenfible quantity of liquid colledfed in them, the furfaces
“ confequently quite contiguous to each other, it fbould not
“ be very apparent, and might therefore be overlooked by
“ one prepoflefled with the idea that no natural communica-
“ tion did there exift. But I have never feen the Brain in
“ fuch ftate, but that it was very eafy to perceive it. When
“ water is preternaturally colledled in the Lateral Ventricles,,
“ it is fometimes obferved to be contained in much greater
“ quantity in one of them, than in the other ; and I have-
“ feen one of the Ventricles much enlarged and full of water,
“ v/hile the other remained of its natural capacity and con-
“ rained hardly any water. This appearance I fliould, how-

C ever,

OF THE COMMUNICATION BETWEEN

“ ever, impute, not to the obliteration or obflrudion of the
** communication betwixt them; but to one fide of the Brain
having been more affeded with difeafe, more flaccid and
“ tender, than the other ; in confequence of which, a greater
“ exfudation had taken place from the veflels of this part,

and the fides of the Ventricle had yielded more readily to
the preffure of the water as it was eflufed.

I remain, with much refped and efteem,

Dear Sir,

Edinburgh, **
i \th Auguji 1794. JT

“ Your mofl obedient humble fervant,

il D. Rutherford.”

As the Human Anatomy is generally illuftrated by a Com-
parifon with other Animals, I next diffeded the Brain of the
Ox and of the Sheep, in the fame manner ; of which Mr
Fy fe drew accurate Figures. Thefe were compared with the
Diffeded Brains by three of my Colleagues, to wit, Dr Gre-

gorv,

THE VENTRICLES OF THE BRAIN.

gory, Dr Rutherford, and Dr Duncan ; who allow me to
add, that they were equally fatisfied with the Accuracy of
thefe Figures.

I found, that in thefe Animals, (and I have fmce obferved
the fame in the Horfe and in the Whale), the middle parts
of the Thalami Nervorum Opticorum are incorporated inti-
mately, and hence, from the Paffage by which the Lateral
Ventricles communicate with each other and with the Third
Ventricle, there is a Paflage above, as well as below, the
joining of the Thalami.

As this joining, and all other circumflances of the ftruc-
ture, are fo nearly the fame in the Ox, the Horfe, and the
Sheep, I think it fufficient to publifli the Figure taken from
the Ox.

G 2

EXPLA

OF THE COMMUNICATION BETWEEN

EXPLANATION

OF THE

TABLES.

In the defcription I am about to give of thefe Tables,
I fhall place the Letters to which I refer, on an Outline of
the Tables.

Explanation of Table Firft.

This Table reprefents the Human Cranium and Ence-
phalon, cut perpendicularly at the right lide of the
Falx and Septum Lucidum.

A A Reprefents the Sedion of the Cranium.

B A Sedion of the Right Frontal Sinus.

TAB. I.

-*-■

• '■

THE VENTRICLES OF THE BRAIN,

G The Forepart of the Falx, fixed to the Crifia
Galli.

D The Backpart of the Falx, fixed to the Middle of the
Tentorium, E.

F The Upper and Anterior Part of the Cerebellum.

G Part of the Inner-fide of the Left Hemifphere of the

Brain, with Arteries upon its furface from the An-
terior Branch of the Internal Carotid Artery.

H H A Se&ion of the Corpus Callofum.

I I The Septum Lucidum, between the Lateral Ventricles,
in which there is no Hole.

K The Middle Part, or Body, of the Fornix.

L A Se&ion of the Right Pofierior Crus of the For-
nix.

22 OF THE COMMUNICATION BETWEEN

M A Section of the Right Anterior Crus of the For-
nix.

N The Left Anterior Crus of the Fornix.

O A Se&ion of the Anterior Commifliira Cerebri.

P The Inner-fide, of the Left Thalamus Nervi Optici,
forming the Left Side of the Third Ventricle.

A Vein running on the Right Side of the Forepart of
the Septum Lucidum, and then acrofs the Forepart
of the Body of the Fornix, to terminate in the Cho-
roid Plexus, R, under the Body of the Fornix, to
which the Choroid Plexufes of the two Lateral Ven-
tricles are united.

S An Oval Hole, fituated under the Anterior Part of
the Body of the Fornix ; behind the Anterior Crura
of the Fornix and Commiilura Anterior Cerebri ; on
the Forepart of the Joining of the Choroid Plexufes
of the two Lateral Ventricles of the Brain ; and
over the Forepart of the Third Ventricle. Hence,

THE VENTRICLES OF THE BRAIN.

at this place, the Lateral Ventricles of the Brain
communicate with each other and with the Third
Ventricle.

The Left Optic Nerve cut away from the Right at
the place of their Jundion.

A Blind Sac in the Left Side of the Third Ventricle ;
under the Commifiura Anterior, and between the
Continuation of the Corpus Callofum and the Join-
ing of the Left Optic Nerve with its Thalamus.

The Iter per Infundibulum ad Glandulam Pituitariam,
between the Joining of the Optic Nerves with their
Thalami and the Corpora Albicantia ; a Sedion of
the Right one of which is reprefented at W»

A Sedion of the Tuber Annulare.

The Pineal Gland, fixed by a Peduncle on each fide
to the Thalami Nervorum Opticorum, and by a
middle Peduncle to Z, the Commifiiira Cerebri
Pofierior.

OF THE COMMUNICATION BETWEEN

The Nates of the Right Side cut.

The Teftis of the Right Side cut.

The Iter a Tertio ad Quartum Ventriculum.

A SeClion of the Right Internal Carotid Artery.

Explanation

' \

THE VENTRICLES OF THE BRAIN.

Explanation of Table Second.

This Table reprefents the Cranium and the Left He-
mifphere of the Brain of the fame fubject ; cut,
firft, perpendicularly, about the diflance of a finger-
breadth from the Falx, to fuch a depth as to lay
open the Left Lateral Ventricle 3 and then cut, al-
moft horizontally, from the Septum Lucidum and
Left Ventricle, to the Outer-fide of the Left Hemi-
fphere of the Brain.

A The Sagittal Suture of the Cranium.

B B The Cut Edge of the Top of the Cranium.
C C An Horizontal Section of the Cranium.

D D

OF THE COMMUNICATION BETWEEN

D D The Left Side of the Falx.

E E The Inner- part of the Left Hemifphere, cut perpen-
dicularly.

e e The Outer-part of the Left Hemifphere, cut almoft
horizontally.

F F A perpendicular Section of the Corpus Callofum.

G The Septum Lucidum.

H The Middle Part or Body of the Fornix.

I Part of the Anterior Cornu of the Lateral Ventri-
cle.

K The Poflerior Cornu of the Lateral Ventricle.

L The Left Pes Hippocampi.

M A Sedion of the Left Corpus Striatum.

THE VENTRICLES OF THE BRAIN.

N A Se&ion of the Left Thalamus Nervi Optici.

O The Choroid Plexus of the Left Ventricle.

R Veins running on the Forepart of the Septum Luci-
dum, which pafs over Q^, the Left Anterior Crus
of the Fornix, to terminate where the Choroid
Plexufes of the Two Ventricles are joined to the
Choroid Plexus under the Body of the Fornix.

S The Left Side of the Oval Hole or Paffage by which
the Lateral Ventricles communicate with each other
and with the Third Ventricle.

D 2

Explanation

OF THE COMMUNICATION BETWEEN

Explanation of Table Third.

This Table reprefents the Cranium and the Ence-
phalon of an Ox, cut perpendicularly on the Right
Side of the Falx Cerebri.

A A A Section of the Cranium.

B B The Falx, which is narrower in proportion to the
Brain than it is in Man.

C The Inner - fide of the Left Hemifphere of the
Brain.

X) D A Se&ion of the Corpus Callofum.

TAB. Ill

THE VENTRICLES OF THE BRAIN.

E The Septum Lucidum.

F The Middle Part, or Body, of the Fornix.

G The place from which its Right Pofterior Crus was

cut off.

H A Section of its Right Anterior Crus.

L A Sedicn of the Anterior Commillura Cerebri.

M A longitudinal Se&ion of the Right Olfadory Nerve,
from its Origin to the Ethmoid Bone.

N A Canal, or Tube, which begins in the Forepart of
the Lateral Ventricle, and is continued obliquely
downwards within the Optic Nerve, enlarging near
to the End of the Nerve. The Inner- fides of it
ar'e medullary ; and the End of it, which is fhut
or blind, is covered with a cineritious Bulb, O ;
“from which the Fibres of the Olfactory Nerve are
derived.

3°

OF THE COMMUNICATION BETWEEN

P A thick Medullary Cord cut, by which the Thalami
of the Optic Nerves are united*

The Choroid Plexus under the Body of the For-
nix.

R An Oval Hole by which the Lateral Ventricles com-
municate with each other and with the Third
Ventricle.

S A Palfage leading downwards, between the Anterior

Commiffura Cerebri, and the Joining or Commiflura
of the Thalami Nervorum Opticorum.

T A Sedion of the Right Optic Nerve where it is

joined to its Fellow.

U A Sedion of the Right Corpus Albicans.

V The Infundibulum, between the Joining of the Optic
Nerves and the Corpora Albicantia.

THE VENTRICLES OF THE BRAIN. 31

W A Se&ion of the Tuber Annulare.

X The Pineal Gland.

Y A Se&ion of the Right Nates.

Z A Se&ion of the Right Teftis.

* A Sedlion of the Cerebellum.

a A Section of the Commiflura Cerebri Poderior.

h A Paflage, from the Hole by which the Lateral Ven~
tricles communicate with each other and with the
Third Ventricle, leading to c, or to the Iter ad
Quartum Ventriculum.

d The Cavity of the Fourth Ventricle.

e The Spinal Marrow, confiding of two principal
Cords.

32 OF THE COMMUNICATION, &c.

/ The Bottom of the Fourth Ventricle, fhut by its
Choroid Plexus and Pia Mater ; fo that there is
no Communication between the Cavity of the
Fourth Ventricle and the Cavity of the Spinal
Marrow.

CHAP.

<►

OF THE COMMUNICATION BETWEEN

32*'

Explanation of Table Fourth. *

In this Table, the Septum Lucidum, and the Fornix, im-
mediately behind its Anterior Crura, are cut acrofs, in order
to Ihew, hill more fully, the Paflage by which the Lateral
Ventricles of the Brain communicate with each other and
with the Third Ventricle.

H H A Longitudinal Section of the Corpus Callofum, on
the Right Side of the Septum Lucidum.

I I The Septum Lucidum.

K A Se&ion of the Septum Lucidum, and of the Body
of the Fornix, behind its Anterior Crura.

L The Right Anterior Crus of the Fornix.

M The Joining of the Choroid Plexufes of the Lateral
Ventricles.

N- A Part

32* THE VENTRICLES OF THE BRAIN.

N A Part of the Left Taenia, or Left Centrum Semicir-
culare Geminum.

O The Sedtion of the Commiilura Cerebri Anterior.

P Part of the Cavity of the Left Lateral Ventricle.

The Bottom of the Paflage by which the Lateral
Ventricles communicate with each other and with
the Third Ventricle.

R The Joining of the Thalami Nervorum Opticorum, cut.
S The Left Side of the Third Ventricle.

T The Pafiage downwards to the Infundibulum.

U The Outline of the Pineal Gland.

V W The Outline of the Right Natis and Teflis, cut.

X The Sedtion of the Commiflura Cerebri Pofterior.

Y The Iter ad Quartum Ventriculum.

CHAP,

CHAP. II.

Of the Situation of the Water in the
Internal Hydrocephalus.

A N Anatomifl, reafoning a prior e , would be apt to fup-
^ pofe, that the Water, in the Hydrocephalus Internus,
fhould be as often found immediately within the Dura Ma-
ter, between it and the Outer-fide of the Brain, Cerebellum,
and Spinal Marrow, as within the Ventricles of the Brain.
Experience, however, proves that it is generally collected
within the Ventricles ; and, as I have not met with a fingle
inftance in which the Water was entirely on the Outer-fide
of the Brain, (although I am far from doubting of the pof-
fibility of the fad), I cannot help fufpeding that this hap-
pens much more rarely than is fuppofed by Authors ; and
that in many cafes, fuppofed to have been of this kind, the

E Brain

34 SITUATION OF THE WATER IN HYDROCEPHALUS.

Brain had been lacerated in opening the Cranium, and the
Water by that means efFufed on the Surface of the
Brain.

In many other cafes, where a great quantity of it was
colledled within the Head, although part of it was, during
life, lituated on the Outer-lide of the Brain, and run out
as foon as the Dura Mater was cut ; it is certain that the
Water had begun to collect within the Ventricles of the
Brain, and had efcaped from them afterwards in confequence
of Changes in the Solid Texture of the Brain, which 1 fhall
endeavour to prove, in the next Chapter, frequently take
place.

CHAP.

CHAP. III.

Of Changes produced in the Texture of
the Brain and Cerebellum, in confequence
of Hydrocephalus Interims.

np1 H E difeafe named Internal Hydrocephalus, in which
the Water is at firft contained within the Ventricles
of the Brain, has been divided by fome Authors, not impro-
perly, into two fpecies j, the Acute , and the Chronic.

In the Acute, the difeafe generally proves fatal in lefs
than, the fpace of a month ; and it is feldom that more than
two or three ounces of Water are found within the Ventri-
cles. From the fmallnefs of the quantity, no uncommon fe-

E 2 paration

CHANGES PRODUCED IN THE BRAIN

paration of the bones from each other, or opening of the
futures, is diftinguifhable.

In the Chronic fpecies of the difeafe, the patient furvives
for many months, fometimes for a year or two. The bones
of the Cranium are feparated from each other ; in fome
cafes to a great diftance. In the foft fpaces between them,
the undulation of a fluid is more or lefs diftinguifhable, ac-
cording to the age of the patient and progrefs of the dif-
eafe. In a few cafes, I have feen the bones feparated to a
conftderable diftance from each other, although the difeafe
did not begin till the child was upwards of two years of
age.

In this fpecies, from two to five pounds of Water have
often been found within the Cranium ; and fometimes a
much greater quantity

When

* See Bonet* Sepulchr. L. i. S. 16. Morgagni, Ep. xii. Lieutaud, L. 3. S. 5.
•and others.

BY INTERNAL HYDROCEPHALUS,

When one, two, or three pounds only of Water were col-
lected, it has been generally confined within the Ventricles
of the Brain ; the fides of which, or fubftance of the Brain
bounding the Ventricles, were obferved to be much thinner*
than they are in health : And as the Bones' at the top of

the Cranium are more loofely connected than thofe at its
bafe, the Sub fiance of the Brain which covers the Ventri-
cles, or the upper part of its hemifpheres, is in proportion
more dilated than the under part of the Brain. In fome
inftances, the Subfiance of the Brain appeared to be forae-
what indurated ; in others, it feemed to be foftened.

Where the quantity of Water amounted to five, fix, or
more pounds, partial Adhefions of the Surface of the Brain
to the Dura Mater were obferved ; at the fame time, a
quantity run out on opening the Cranium and Dura Mater f.

* Morgagni, Ep. xii. 5. “ Cerebrum Hydrocephalo attenuatum.” 8. “ Parietum
“ Lateralium Ventriculorum craffitudo vi aquse extenuata.” Lieutaud, L. 3.
Obf. 322. “ A mole aquae, Cerebrum in ambitu femipollicis craffitiem vix fuper-
“ abat.”

+ Morgagni, Ep. xii, 6, “ Aqua ad primam cultri impreflionem, cum impetrv
“ prorumpena.”

CHANGES PRODUCED IN THE BRAIN

On examining farther, the Cortical and Medullary Subftan-
ces were found to be greatly diminifhed in their bulk and
weight. In fome cafes, after an enormous Diftenfion of the
Ventricles of the Brain, large portions of the folid Subftance
of the Brain feemed to have been deftroyed ; and hence,
the Water was partly lodged within the Ventricles, and
partly between the Surface of the Brain and the Dura
Mater

In other cafes, little remained of the Brain, except its
invefiing membranes, with fome of the fuperficial matter ad-
hering to them ; and the offeous matter of fome of the
bones of the Cranium, was found to be likewife wafted f.

* In a cafe of a Child (C. Gilles, 18 months old,) which occurred in our In-
firmary in 1778, five pounds of Water were found, partly within the Ventricles,
and partly between the Dura Mater and Brain. The Subftance of the Brain ap-
peared foft and flabby ; and its texture, in many parts, was much deftroyed.

+ Lieutaud, L. 3. Obf. 326. Mifcel. Cur. Tredecem Aquae librae intra Ven-
triculos et totum Cerebrum nonnifi faccum referebat. — 327. Ex Hildano Aquae

librae

BY INTERNAL HYDROCEPHALUS.

In a foetus Calf, within a few days of the common time
of parturition, I found the Cranium enormoufly dilated, and
nearly of a fpherical figure. On opening the Cranium and
Dura Mater with great care, I found the Arachnoid Coat
with the Pia Mater, both of the Brain and Cerebellum, in
contad with the Dura Mater, and in fome places adhering
to it. On cutting thefe, I found thin and broken-like por-
tions of cineritious -looking fub fiance adhering to them ; and,
within this, upwards of fifteen pounds of a tranfparent wa-
tery liquor, a fmall proportion only of which coagulated on
boiling it. I afterwards cut out all the membranes of the
Brain and Cerebellum, with the cineritious-looking matter
adhering to them, and found that the whole weighed only
one ounce and a half.

librae ofto : ipfummet Cerebrum in facculum extendebatur, Cranium paffim mem-
branofum, potius quam offeum, videbatur. — 328. Cerebrum in faccum exienfum. —
329. Aquae copia Cerebrum ferine obliterabat.— -332. Ex Kerkring. Cerebri loco.
Aqua.

Morgagni, Ep. xii. 5. Cerebrum Hydrocephalo attenuatum. — 8. Cerebrum
priroa infpectione nudum eke videbatur, cum, iniiar crallioris membranae, adhaeref-
ceret undique arcu.uae diffolutorum oikum circumferentiae, — 8. Radicem Cerebri
in fibras cinfiuxike.

4°

CHANGES PRODUCED IN THE BRAIN, &c.

In Sheep labouring under the difeafe commonly called the
Staggers, I have found a Bag, containing a watery fluid, and
bodies which have been luppofed to be animated, (and which
I have no doubt are fo), in one of the hemifpheres of the
Brain. Over the Bag, the bottom of which was connected
to the bottom of one of the Lateral Ventricles, I found the
Medullary and Cineritious Subflances of the Brain confumed,
and the Bag adhering to the Pia Mater, and the Pia Mater
with the Arachnoid Coat adhering to the Dura Mater ; and
over that part of the Dura Mater, the ofleous fubflance of
the Cranium was wanting, and a membrane feemed to fupply
its place. On inquiry, I find, that Sheep-graziers diftinguifli
with certainty the fituation of this difeafe, by feeling a foft
place in the Cranium, at which they make a perforation, and
endeavour to extrad the Sac or Bag ; but, as the fubflance
of the Brain is deeply affeded by the difeafe, few are faved
by the operation.

CHAP.

CHAP. IV.

An Attempt to prove, that the Changes
in. the Texture of the Brain and Cere*
helium, in consequence of Internal Hy-
drocephalus, are produced by the Ab-
forbent Veffels.

IT T has been, fo far as I know, the univerfal opinion
of Anatomifts and Phylicians, that, in the Hydro-
cephalus Internus, the Subdance of the Brain is melted
down by the Watery Liquor which is effufed from the
Arteries,

To-

CHANGES IN THE BRAIN HOW PRODUCED.

To fhew that they have thought fo, I (hall, at the foot of
the page, fubjoin a few quotations from fome of the moft
eminent Authors

* Boneti, Sep. L. i. S. 1 6. Obf. n. “ Nam potuit Cerebrum per redundans
11 ferum adeo fuifle emollitum ut mucus effe vifum fuerit.” S. 1 6. Ad. Obf. J.
“ Radix Cerebri, a perpetuo illo diluvio et feri incubitu, in fibras diffluxiffe vide-
“ batur.”

'Morgagni, de Sed. et Cur. Morb. Ep. xii. 5. “ Cerebrum in Hydrocephalo at-
“ tenuatum et in aquam refolutum.” — 6. “ Quod fi Cerebrum fit Hydrocephali
“ aqua diffolutum.” — 6. Verum quacunque ratione et quocunque ex fonte intra Ce-
« rebri thecam aqua praeter naturam congeratur fane poterit, fi necdum illud con-
il creverit, ejus concretionem fuo mterjeQ:u prohibere : aut fi jam concreverit ; inter
“ ejus particulas fe infinuando, has fenfim magis magisque disjungere, donee ad mi-
“ nimas ventum fit, facile cum aqua permifeendas, neque amplius internofeendas.”—
6. “ In altero Hydrocephalo non folum disjundlionem propemodum perfedam fed
“ disjunftarum particularum cum aqua permiflionem ipfa indicabit aqua loturse car-
“ nium fimilis, praeterquam et crafluin meningem nihil diftindti in diffluente cerebro
“ videre licuit.’*

Haller, in Elem. Phyf. L x. § xxxix. “ Quod autem, difToluto in aquam Cere-
11 bro et demurn amiffo vivatur,’* &c.

“ Eo modo credibiie ell, fenfim quidem Cerebrum contabuiffe in aquam.”

CHANGES IN THE BRAIN HOW PRODUCED.

As a confequence of fuch an opinion, it fhould follow,
that the Watery Liquor poflefled the farther quality of ren-
dering the white and opaque Medullary Subftance of the
Brain tranfparent ; and, on evaporating the water, the Me-
dullary Subftance fhould remain in the form of an extradh

But, inftead of that, we do not perceive how the water
effufed into the Ventricles is brought in contadt with the
medullary or other fubftance of the Brain, as the Ventricles
are lined with thin but denfe membrane. — We do not find
that we can diffolve the Medullary Subftance of the Brain in
the Watery Liquor we extradf from the Ventricles of the
Brain of a perfon labouring under Hydrocephalus.

When we heat and evaporate the Watery Liquor colledled
in Hydrocephalus, we are fo far from recovering the medul-
lary fubftance of the Brain, that very little coagulable or
folid matter is found in the refiduum ; for the quantity even
of the coagulable lymph is lefs in this than in moft other
fpecies of Dropfy

F 2 Similar

* Boneti, Sep. L. i. S. 1 6. Ad. Obf. 12. De Hydrocephalo, “ Aquse, in
11 cochleari fenec, nonnihil prunis nnpofuimus. Non in gelatinatn concrevit, uti

“ aqua in ventre Hydiopicorum folet, i'ed, poll evaporationem, iai acre reliquit.5*'

CHANGES IN THE BRAIN HOW PRODUCED.

Similar Watery Liquor, effufed in the other fpecies of Drop-
fy, is not found, nor fuppofed, to poRefs any fuch folvent
power.

I apprehend, therefore, that this hypothefis is to be en-

tirely rejeded ; and, that inflead of fuppofing that the parts
of the Brain difappear becaufe they are melted down by the
Water, and rendered pellucid, we are to imagine, that the
parts of the Brain are carried off by the Abforbent Veffels j
which are excited to unufual adion, by the tendon and irri-
tation which the Water occahons.

In a cafe, very different from Dropfy, to which I was

called, in 1784, along with Dr Charles Webster, I have
likewife feen undoubted proof, that a great part of the folid
fub Ranee of the Brain muR have been carried away by the
Abforbent Veflels. The Patient, a Rout man, about thirty
years of age, had, for ten months, complained of the moR
excruciating pain in the right fide of his Forehead. At
laft he was feized with delirium, which terminated in flupor
and apoplexy ; and in this Rate I found him. He died
next day. On opening his Head, the Left Hemifphere of
the Brain was found to have its ufual appearance ; but the

CHANGES IN THE BRAIN HOW PRODUCED.

Anterior Lobe of the Right Hemi'fphere was of a deep pur-
ple colour, very conliderably indurated, and adhered firmly
to the Supra Orbitar Plate. On cutting it perpendicularly
into two parts, which I preferve, the dill inch ion of Cineri-
tious and Medullary Matter was fcarcely ohfervable ; for
the whole of it was of a dark purple colour, nearly uniform
in texture, and had large and numerous veflels, filled with
red blood, in its compofition refembling the Lungs in an in-
flamed flate more than the Brain.

There was no effufion of water or of blood, nor collection
of purulent matter. It was therefore evident, that, in pro-
portion to the enlargement of the Blood-vefiels, and perhaps
increafe of their number, there mult have been an Abftrac-
tion of the Cineritious and Medullary Matter made by the
Abforbent Veflels.

As the Cortical and Aledullary Subftances of the Brain
are not evidently compreflible, it follows, that in the cafes
of Sudden Apoplexy, Epilepfy, Suffocation from Noxious Va-
pours, Drowning, Hanging, there can be no fuch fenfible
general Enlargement of the Blood-vefiels as has been fuppo-
fed and defcribed by Authors. But if, by long-continued

intemperance,

46 CHANGES IN THE BRAIN HOW PRODUCED.

intemperance, or other caufes, the Blood has been circulated
within the Head with more than ufual violence, there may
have been an increafed Abforption or Wafting of the folid
Subftance of the Encephalon ; and, in proportion to that,
an Enlargement of the Blood-veflels, and evident Increafe of
the Quantity of Blood within the Head.

CHAP.

CHAP. V

Circumftances enumerated, which prove,
That the Solid Parts compofing the

fbrbed.

rT1HAT the Solid Matter of the Brain can be carried off
by the Abforbent Veffels, appears, at firft fight, an opi-
nion fo incredible, that I fhall endeavour to fupport it by
the following Obfervations, — which, I apprehend, prove be-
yond a doubt, that the Solid as well as the Fluid Parts of
Animals are under a conftant date of Change.

of our

(i% The

4b proof that the solids are absorbed.

a. The Several Glands and Glandular Vifcera are often
enlarged and indurated, remain in that Rate for a confider-
ahle time, and fometimes return to their natural Rze and re-
cover their found Rrudture.

b. Hemorrhoidal Tumours, which I have found to con-
tain a great deal of folid matter, inflead of being entirely
produced, as Morgagni and Haller have affirmed*, by a
varicous Rate of the Veins, after increaRng to conRderable
bulk, difappear almoR entirely, leaving nothing but the fkin
which covered them.

c. Venereal Excrefcences, called Fici, Mori, &c. are often
removed by the internal ufe of Mercury.

d. The glandular body called Thymus, generally difap-
pears, or is abforbed, before the fixteenth year of life.

e. Where

* Morgagni, Ep. xxxii. io, ir.

Haller, El. Phyf. T. vii. lxxiv. S. iv. § xii. p. 193.

PROOF THAT THE SOLIDS ARE ABSORBED.

e. Where the Skin is extended, and at the fame time ir-
ritated, by an abfcefs forming under it in the condenfed
cellular fubftance, it is wafted, and fometimes breaks into
holes, feveral days before the purulent matter contained in
the abfcefs is difcharged, that is, before the matter is in
contad with the ftdn.

f. In like manner, the Flefhy Parts of the Mufcles fome-
times ftirink greatly, lofe their red colour and fibrous ap-
pearance, and feem to be converted into white-coloured
tough membranes. I have long had in my poflefllon a pre-
paration, in which a large portion of the Apex of the Left
Ventricle of the Heart of a Man has entirely loft its Flefhy
Strudure, and has the appearance of a white, tough, thin
membrane. Within this part is contained a whitifh firm
Grume formed by the blood, fuch as is found in Aneuriftnal

Sacs. In other inftances, the whole Flefhy Part of a

Mufcle is removed, without the application to it of fluid or
acrid matter, which could be fuppofed to have corroded or
melted it down into a liquid ft ate. A remarkable example

of this kind occurred about twenty years ago, in the cafe

of an eminent Phyfician, Dr Au -n, whom I attended

along with Dr Hay and the late Dr Hope, and who, for
upwards of a year before his death, had been diftrelfed with

pains,

PROOF THAT THE SOLIDS ARE ABSORBED.

pains in the inteflines. On opening his body, we found,
to our furprife, that the diftended Sigmoid Flexure of the
Colon was firmly united with the Skin, and that the Abdo-
minal Mufcles were entirely removed from a fpace larger
than the whole hand could cover.

In Old Perfons, I have repeatedly found, that the Cavities
of fome of the Burfee Mucofae which are contiguous to Liga-
ments, communicated with the Cavities of the Joints, in con-
fequence of a Wafting of the Membranes of the Burfas and
Ligaments. Thefe Perfons had not, in life, complained of
pain ; no acrid, purulent, or other liquor, was collected ;
the fides of the holes by which the communications were
made, were not ragged, but fmooth ; no lacerated membranes
were found floating in the Burfse or in the Joints : The

Wafle, therefore, could only have been produced by the gra-
dual Abforption of the Particles which had compofed the
Membranes.

g. But the moll ftriking proofs that the Solids may be Ab-
forbed, are to be drawn from attention to the Structure and
Growth of the Bones, and to their Wafle by age and difeafe.

h. When Powder of Madder is mixed with the ordinary
food of an Animal, it communicates its colour to the clear

part

PROOF THAT THE SOLIDS ARE ABSORBED.

part of the Blood, and foon thereafter the Bones are tinged.
The Red Colour of the Bone, in forae degree, depends on
the Particles of the Madder mixed with the Blood in the
Veffels of the Bone ; but as I have found, that the Colour
is little, indeed not fenfibly, changed by injeding pure wa-
ter into the Veffels, and wafhing the Blood out of them, it
is certain, that the Colour is chiefly owing to a Red Earthy
Matter which has been added to the Bones whilfl: the Ani-
mal was fed with the mixture of Madder. If the Madder
be withdrawn from the food of the Animal, the Red Colour
difappears, which can only be by its Abforption.

i. The Skeleton of a very Old Perfon is fo much Lighter
than that of a middle-aged perfon of the fame ftature, that
the difference cannot be accounted for on the common fup-
pofltion that the Solids are compaded, and the Fluids alone
abforbed.

k. On comparing a conflderable number of Sculls of very
Old Perfons, with an equal number of thofe of Middle Age,
I have found, that they had loit about Two Parts of Five
of their Weight.

G 2

L In

PROOF THAT THE SOLIDS ARE ABSORBED.

/. In the Jaw-bones of Old Perfons, befides their general
lofs of weight in common with the other bones, the Sockets
of the Teeth, after thefe drop out, are removed entirely ; fo
that the Lower Jaw-bone lofes nearly one half of its depth,
and, upon the whole, more than one half of its weight.

in. In the Aneurifm of the Arch of the Aorta, of which
many cafes are in my pofleilion, the Sternum, the Ribs, their
Cartilages, the Cartilages of the Trachea are altered in their
fhape, and wafted in their fubftance, long before the Blood
gets into contact with them $ which muft be owing to an
increafed Abforption.

n . In Venereal Cafes, the Bones fometimes fwell confi-
derably, or Nodes form upon them, both of which effects
are often difperfed by Mercury.

o. In a very large collection of Morbid Bones in my poft
feftlon, whilft, in many inftances, their thicknefs and weight
are much greater than in found bones, in others, their
weight is greatly diminiftied.

p. In fome cafes of Ulcerous Caries affecting the lower
end of the Tibia and Joint of the Ankle, I have found, af-
ter

PROOF THAT THE SOLIDS ARE ABSORBED.

ter amputation was performed, that the Bones of the Tarfus
and Metatarfus, at a diilance from the ulcer, were much
Softer and Lighter than in a found perfon of the fame
age.

q. In Rickets, although the Bones, and particularly their

Extremities, are enlarged, yet the Skeleton of a Rickety
Child is commonly Lighter than that of Children of the
fame age who are killed by other difeafes.— — In fome cafes
of Rickets, the Bones become not only thicker but heavier
than in the found date : In proof of which, I have in my

polTeflion the Parietal Bones of a Rickety Perfon which are
upwards of an inch in thicknefs.

r. In the difeafe called Incarnation of Bones, becaufe
they are foft and may be cut like flefn, the Bones become
femitranfparent, and extremely light ; and, in fome cafes,
whilft thefe changes were going on in them, it was obferved
that the Urine depolited a large quantity of a White
Plaftery-looking Sediment ; to which is added, in one cafe
of a Woman, of the name Sue, that before the difeafe be-
gan, fhe had been in the habit of devouring daily a great
quantity of Sea-falt. There can be no doubt, therefore,
that, in this difeafe, the Earthy Matter of the Bones is car-
ried

54 PROOF THAT THE SOLIDS ARE ABSORBED.

ried off by the Abforbing Veflels : In confequence of which,
thofe Bones, or Parts of Bones, which naturally are the
hardefi:, or have the greateft quantity of Earth in their
compolition, are by this difeafe rendered the fofteft.

f. From the whole, it appears, not only, that the Solid
Parts of the Body may be xAbforbed in confequence of Dif-
eafe j but, that in Health, and during the whole Courfe of
Life, there is fuch a conftant Interchange of the Particles
which compofe the Solids, by means of the Veffels which
Secrete and Abforb, as to render it doubtful whether a An-
gle Atom remains in our Bodies which formed a part of
them fome years ago.

CHAP.

CHAP. VI.

At what Time the Circumftances enu-
merated in the laft Chapter were firft
taught by the Author.

late years, the Abforption of the Solid Parts of Ani-
mals has been mentioned by a few Writers who have
publifhed in London : And as Mr John Hunter has been
quoted by fome of them, as the Author of this Do&rine, I
muft here obferve, that fo far back as the year 1759, and
ever fince that time, I have mentioned, in different parts of
my annual Courfe of Lectures in this Univerfity, all the Cir-
cumftances above mentioned which relate to the Bones, and

likewife

56 WHEN THE AUTHOR FIRST TAUGHT THE

likewife feveral of the CircumBances which appeared to
prove an Abforption of the other Solid Parts and, parti-
cularly, I endeavoured to explain, on this principle, the
Changes which are produced on the Sternum and Ribs by
Aneurifm, which Dr William Hunter, at that time, ac-
counted for, on the erroneous fuppolition, that thefe Bones
wTere melted down by the current and folvent power of the
Blood. See Med. Obf. and Inq. vol. i. 1757, p. 344. “ But

“ in this cafe,” fays he, “ the appearance was rather as if
“ the Blood had infenlibly dilfolved and waflied away the
“ SubBance of the Bone, making greateB havock in the
“ foftefl part of the Bone, as we fee in Bones of unequal
“ texture that have been long wafhed by a dropping, or a
“ Bream of water. Bias the Bone that property which fome
“ have afcribed to it, of diflolving Bony Matter ?” &c.

It is plain, then, either, that Mr John Hunter had not,
at that time, propofed the Doctrine of the Abforption of
OfTeous Matter 5 or, if he did fo, that his Brother was ig-
norant of it, or paid no regard to it.

When, near twenty years thereafter, Mr John Hunter
mentioned fuch an opinion in his Lectures, it appears, from
the teflimony of a very fenfible and ingenious gentleman,

(Dr

DOCTRINE OF THE ABSORPTION OF THE SOLIDS. 57

(Dr Winterbottom), who attended him then, and who, in
his Thelis, has (hewn his difpofition to do him juftice, that
he relied his opinion chiefly, if not folely, on the circum-
Ilance, that in Growing Animals the Medullary Canal is en-
larged in its diameter ; which he took for granted mud be
owing to an Abforption of the Internal Layers of the Bone,
whilft new Layers were adding to its external part j not
knowing that the celebrated Du Hamel has, upwards of
half a century ago, proved by the following Ample and de-
ciflve experiment, That the Diameter of a Bone, as well as
that of its Medullary Canal, is increaflng in Growing Ani-
mals, by an Extenfion of the feveral Layers which compofe
it. See Mem. de l’Acad. des Sc. 1743, p. 102. “ J’en-

“ tourai 1’ Os d’ un Pigeonneau Vivant avec un Anneau de
“ fll d’argent, qui etoit place fous les Tendons et fur le Pe-
“ riofle. Je laiflai la cet Anneau, pour reconnoitre ce qui
“ arriveroit aux couches Ofleufes deja formees, fuppofe
“ qu’elles vinflfent a s’etendre ; car je penfois que mon An-
“ neau etoit plus fort qu’il ne falloit pour reflfter a 1’ effort
“ que ces lames Ofleufes feroient pour s’etendre. II reflfloit
“ en effet ; et les couches Ofleufes, qui n’etoient pas encore
“ fort dures, ne pouvant s’etendre vis-a-vis 1’ Anneau, fe cou-
“ perent. Ce qui prouve bien 1’ Extenfion des Couches Of-
<( feufes, c’efl; qu’ ayant difleque la partie, je trouvai, que le

H “ Diametre

WHEN THE AUTHOR FIRST TAUGHT THE

“ Diametre de l’Anneau n’etoit pas plus grand que celui du
“ Canal Medullaire.” — — To iliew ftill more clearly, .that
Mr John Hunter had built his opinion on an erroneous
foundation, I have remarked, in many Difeafed Bones in
my pofleflion, in which the Thicknefs of the Bones is great-
ly increafed, that the Medullary Canal is much diminifhed.

From this, and from Du Hamel’s experiment, then, we

may obferve, that the Plates of the Bones may be extended
in all directions, or, that they grow in length, breadth, and
thicknefs.

Dr Winterbottom, after attending Mr John Hunter’s
Lectures, ftudied the ufual number of years in this Univer-
fity, and received the Degree of Do6toi\of Medicine, in
1781, after publifhing an excellent DijQertation, De Vafis
Abforbentibus.

In this, p. 27. he writes as follows :

“ § 34. Abforbentia, Fluida forbere, jamdiu notum ; glo-
“ ria autem monftrandi ea Solida quoque haurire, penes
“ Monro Anatomicum peritiffimum eft. In hanc fenten-
“ tiam, uti jamdudum in PraeleCtionibus praedicavit, multis
‘‘ argumentis addublus ibat : Sed praefertim, quia Thymum

“ glandulam

DOCTRINE OF THE ABSORPTION OF THE SOLIDS. 59

u glandulam evanefcere ; Ofla Senis multo leviora quam Ju~
“ venis efle ; Terrain Rubram, quam Rubia Tinclorum in
“ Ofla infert, poll aliquod te'mpus auferri etiamque variis
“ in morbis Ofla mollia, diftorta, fere peliucida, et levia, de-
“ venire ; imo, aliquot in exemplis, infolitam quantitatem
“ Sedimenti Albidi, Terrse Odium limillime, in Urina fuifle
“ inventam, — animadvertit.

“ In Prseledionibus, de eadem re, obfervavit cl. Joannes
“ Hunter, “ Quamvis difficile comprehenfu fit quomodo
“ Vafa poffint Solida amovere, aeque tamen difficile compre-
“ henfu quomodo ea formare poffint, quod niliilo fecius fere
“ omnes credunt.”

“ § 35. Solida non minus quam Fluida abforberi, pro
“ certo affirmare haud cundor ; namque Ofla Hominis, me-
“ dia aetate, plus Ponderis quam Senilia, aeque ampla ha-
“ bent. Quibufdam in exemplis quoque Atrophiae et Tabis,
“ partem offium effie abforptam, inter Audores omnes con-
“ venit.

“ § 36* Hanc rem Joannes Hunter quam pulcherrime
“ fc illuftrat, (*in Praeledionibus) : “ In Offie Femoris In-

H 2 “ fantis,

60 WHEN THE AUTHOR FIRST TAUGHT, &c,

“ fantis, Cavitas initio perexigua eft ; corpore autem cref-
“ cente, amplior evadit : Ita, dum Arteriae Terram Offis

“ externse parti adjiciunt, Abforbentia earn interne ad-
“ imunt.”

Dr Winterbottom adds, in a Note f, “ Hoc aliter ex-
“ plicari pode equidem non nego ; fed opinio modo pod-
“ ta, etfi non omnind certa, pulchra faltem mihi vide-

•n

tur.

CHAP. VII-

Of the Cure of Internal Hydrocephalus
by Medicines.

AS, probably, the Particles compofing the Solids of our
Body are diffolved by Secreted Fluids, or reduced to a
Fluid State before they be fit for being abforbed ; and as,
therefore, the Wade of the Solids, by the Abforption of
them, mull be performed by a much more complex procefs
than that of Fluids ; we ihould, after finding proof that the
Cineritious and Medullary Matter of the Brain can be remo-
ved by it, be apt, at fir ft fight, to fuppofe, that the Internal
Hydrocephalus could be eaftly cured by Medicine. But,

when

OF THE CURE OF HYDROCEPHALUS

when we reflect, that the Diftenfion and Irritation, which
create the unufiial exertion of the Abforbent Syftem, feem to
operate ft ill more powerfully on the Secerning Veffels, and
that whilft the Abforbents are preying on the Solid Matter
of the Brain, the EfFufion of the Watery Liquor is increa-
ling rapidly, we begin to perceive, that the Cure mult be
much more difficult than ave had fuppofed it to be : And,

as we find, by experience, that Irritation greatly increafes
the difcharge from exhaling veffels, I have often thought,
that the lingular Senfibility of the Parts of the Brain, high-
ly excited by the Diflenlion of its Ventricles in Hydroce-
phalus, muft, in it, render the chance of Cure far lefs than
it is in other fpecies of Encyfted Dropfy.

Of late years, Mercury has been much extolled for the
cure of Hydrocephalus Internus ; and various cafes of fuc-
cefs with it, even after the difeafe had made, conliderable
progrefs, have been publifhed.

I fhall fubjoin a Summary Account of the Cafes in which
I have made trial of it.

Since the month of Augufi: 1779, I have attended Twenty-
two Patients, labouring under Internal Hydrocephalus, to whom

BY MEDICINES.

1 have given Mercury. Of thefe, Fifteen were Males,

and Seven Females.' Twelve of them were under Seven

years of age : Nine of them were from Eight to Fourteen

years of age : One was Twenty-three years old. Four

of them lived Five Days only after I was called : Nine of

them furvived Seven or Eight Days : Three of them fur-

vived Ten Days : Five of them furvived Thirteen or Four-
teen Days : One, Six years of age, furvived Four Months,

without any fenlible Enlargement of his Head*

In treating thefe cafes, I generally began with the appli-
cation of Leeches to the Temples. I then gave Calomel, in
fuch quantity as to a6t as a brifk purgative. I applied a
large Blifter to the Top of the Head. In fome cafes, I
kept a portion of the blidered part open as an Iffue. In
others, I applied Blifters in fucceffion to different parts of
the Head. In all of them, I direHed, that ftrong Mercurial
Ointment fliould be carefully rubbed upon the Skin of the
Legs or Arms, morning and evening : And, in feverals, I

added Dofes of Calomel by the Mouth ; taking care not to

give fo much of it as to occalion purging. In fome cafes,

I combined the Powder of Squills with the Calomel ; and in
a few, the Powder of the Digitalis Purpurea.

OF THE CURE OF HYDROCEPHALUS

In Four of thefe cafes, the Gums became Red, but with
little fwelling : In Four others, the Gums were not only
Red, but confiderably fwelled. In Two cafes, there was a
free Salivation. In the Boy, fix years old, who furvived
four months, a profufe Salivation was kept up for feven
weeks ; yet, after his death, Eight Ounces of Water were
found in the Ventricles of the Brain, by Mr Gullon, Sur-
geon in Dunfermline, under whofe care he was after the

Salivation. In none of the other cafes, were the effe&s

of the Mercury diftinguifhable.

As, in the greater number of the above cafes, the difeafe
had made confiderable progrefs before I was called ; and
as moft of the Patients furvived but for a fhort time there-
after ; the Effe&s which the Mercury may have, if given
on the firfl appearance of the fymptoms, are by no means
fully determined. And, as I have repeatedly found, in
other dangerous fpecies of the Natural Encyfled Dropfy,
particularly in Hydrothorax and Afcites, that Mercury, com-
bined with Squills or other diuretic medicines, in fuch quan-
tity as to falivate in a flight degree, contributed much to
the relief or cure of the Patient ; I would recommend the
farther trial of it in Hydrocephalus. At the fame time,

confidering

BY MEDICINES.

confidering the importance, fenhbility, and delicate tex-
ture, of the parts which are affecded, and total failure
in the cafes I have defcribed j I cannot help fufpedding,
that feveral late Writers are much too fanguine in their
expe&ation of removing Hydrocephalus by the ufe of Mer-
cury.

CHAP,

•V

CHAP. VIIL

Of the Cure of Hydrocephalus Interims
by Chirurgical Operation.

~1~7I0UR different States of the Difeafe may occur, which
we fhall confider feparately.

m mw rrmxt&'taL&rzJs

i. If, when the difeafe began, it was not attended with
acute pain, and the other common fymptoms ; for I think there
can be no doubt that the Patient muft buffer much more diflrefs
when the Water is collected within and diftends the Ven-

I 2 tricles,

OF THE CURE OF HYDROCEPHALUS

tricles, than where it is efFufed on the External Surface of
the Brain : and if, from a very evident fluctuation of the

Water, chiefly at the Bregma, it is fuppofed, that the Water
is fituated immediately within the Dura Mater, between it
and the Surfaces of the Brain, Cerebellum and Spinal Mar-
row : we ought to punCture the Dura Mater ; as this can

be done without danger, may give immediate relief, and may
have fome chance of producing a cure. The Dura Mater
ought to be punCtured cautioufly with a Lancet, at the fide
of the Bregma, or as far as pollible from the Superior Lon-
gitudinal Sinus.

In my Book on the Nervous Syftem, Chap. iv. SeCt. 3.
I have given the hiftory of one attempt of this kind, which
I directed , and fhall here refer the Reader to it.

2. If the Water be collected, in fmall quantity, within
the Ventricles, which is almoft always the cafe in the
Acute Hydrocephalus, the deep Wound of the Subftance
of the Brain, which mufl be inflicted in order to reach the
cavity of the Ventricles, would probably prove fatal direCt -
ly, or indireCtly by exciting inflammation : or, if it fliould

neither

BY OPERATION.

neither immediately prove fatal, nor excite inflammation,
the Water would foon be again collected ; and, of courfe,
the difeafe would, ere long, terminate in death.

3. *In the Chronic Species of Internal Hydrocephalus,
where the Head is enlarged by Water, which has been gra-
dually collecting, and is ftill entirely confined within the
Ventricles of the Brain, fome Authors have propofed, and,
in a few cafes, have ventured, to difcharge the Water by
pundture with a Trocar. But, within a few hours after
the operation, every one of their Patients died *.

Upon

* Ep. Ferdinandus, HUE 1611 “ Hydrocephalutn infantis incidit, funefio

“ eventu.” ^

G. Fabricius, Gent. iii. Obf. 17. “ Ab Hydrocephalo incifo, aperto Bregmate,

“ mors.”

D. Panarolus, in Iatrolog. “ In Hydrocephalo, a perforations cranii mors.”

Wepfer

7°

OF THE CURE OF HYDROCEPHALUS

Upon the whole : When we confider the various dangers

which muft arife from the pun&ure of the fubftance of the
Brain ; from the unequal bending, preffure, and perhaps la-
ceration of parts, which muft happen when the Brain col-
lapfes ; from the admiftion of the air ; from the impoflibi-
lity of adapting the Cranium exa&ly to the Brain for its
fupport, by the application of any bandage j — no prudent
Surgeon will embark himfelf in fuch an attempt, — “ Ne,
“ quern fervare non potuit, occidifle videatur.”

4. If the Water, after having been colledted and confined
within the Ventricles of the Brain, fhall have made its way
out of thefe, in confequence of the deftru&ion of fome of
the Solid Subftance of the Brain by the Abforbent Veflels,
fo as to be lodged, in part, between the Outer Surface of

the

Weffer, Obf. 49. “ Hydrocephalus, in Puella quinque annorum, infeliciter

“ fe£tus.”

“ Muraltus fruftra tentavit curationem Hydrocephali incifi.”

Le Cat. Phil. Tr. Vol. xlvii. Art. 40.

BY OPERATION-

the Brain and the Dura Mater, although it may be difcliar-
ged by a pun&ure of the Common Teguments and Dura
Mater only ; yet, as the fubftance of the Brain has been
materially injured by the difeafe, the cafe is evidently, in
all other relpedls, more delperate than the former.

THE END OF TREATISE FIRST,

• \

MISCELLANEOUS

OBSERVATIONS

ON THE

STRUCTURE AND FUNCTIONS

OF THE

EYES,-

ALEXANDER MONRO, M. D.

PROFESSOR OF MEDICINE, ANATOMY, AND SURGERY,
IN THE UNIVERSITY OF EDINBURGH.

s- ■

EDINBURGH :

PRINTED BY ADAM NEILL AND COMPANY,

1797*

A Table of the Contents of

INTRODUCTION,

Treatife II.

Page

CHAP. I.

Of the Capfule of the Vitreous Humour, - 79

CHAP. II.

Of the Cryftalline Lens, - - 83

Sect. I. Of the Capfule of the Lens, - - - ib,

II. Of the Samdure of the Body of the Lens, and Whe-
ther the Fibres which enter into its Compofition
are Mufcular ? - - - - 85

— — — HI. Of the Refractive Power of the Lens, - 87

CHAP. III.

Of the Optic Nerves and Retina, - 91

Sect. I. Of the Joining of the Optic Nerves, - - ib.

4 II. Of the Infenfibility and Excentricity of . the Optic

Nerves at their Entrance into the Eyeballs, - 92

- — - III. Of the Texture of the Retina, - - 93

— — IV. Of the Termination of the Retina, 94

CHAP. IV.

Of the Choroid Coat and its Ciliary Procefles, 103
CHAP. V.

Of the Iris, - - 107

Sect. I. Of the Bloodveffels of the Iris, - - ib.

■ II. Of the Nerves of the Iris, - - - 109

— III. Of the Mufcular Strudure of the Iris, - - no

CHAP.

76 CONTENTS OF TREATISE II.

CHAP. VI.

Page

Of the Veflels of the Cornea, - 117

CHAP. VII.

Of certain Laws, by which we judge of the Pofition
and DifLance of Objeds, and by which we regulate
the Motions of the Eyes, - - - - 119

CHAP. VIII.

Of the Means by which the Eye accommodates itfelf
to the Diflances of Objects, - - - 125

Sect. I. Of the Effects of the Fibres of the Cryftalline Lens, 126

— — - II. Of the Effects of the Ciliary Procefies of the Choroid

Coat, - - - - - 127

" IIL"l0f the Effects of the Iris,. - 128

IV. J

-= — - V. Of the Effects of the Redi Mufcles, - - 129

- — — VI. Of the Effects of the Oblique Mufcles, - 131

VII. Of the Effeds of the Orbicularis Palpebrarum, - 132

VIII. Conclulion on this Subjed, - 137

CHAP. IX.

Of the Lachrymal Paffages, - 139

Sect. I. Of the Duels of the Lachrymal Gland, - ib.

II. Of the Punda Lachrymalia, and Duds from them to

the Nofe, - - 141

III. Of the Dudus Incifivi, - ib.

Explanation of the Tables, - 145

TREATISE

TREATISE SECOND:

OF THE EYES.

INTRODUCTION.

TN this Paper, I fhall briefly Rate Tome material circum-
fiances, refpecling the Structure and Functions of the
Eyes, which have efcaped the obfervation of Authors ; or,
concerning which, erroneous opinions have, I apprehend,
been entertained by them : And I fhall begin with Remarks
on the Humours of the Eye, and from thefe fhall proceed
outwards, as I have found that a Demonftration or Defc op-
tion in this order is the moffc intelligible.

C H A P,

♦

CHAP. I.

■nr

Of the Capfule of the Vitreous Humour.

H|P FIE Capfule of the Vitreous Humour, from the Bottom
of the Eyeball till it gets forwards as far as to the
Roots of the Ciliary Procefles, is fo extremely thin and deli-
cate, that it can fcarcely be demonftrated by Diffedtion ; and,
fo far, it has very little adhefion to the Retina which covers
it.

Within the Roots of the Ciliary Proceffes, it adheres
clofeiy to the Retina ; and, a little farther forwards, it feems
to divide into two diftindt Layers. The External continues
to be glued to the Retina, and accompanies it to its termina-

K 2 tion,

So OF THE CAPSULE OF THE VITREOUS HUMOUR.

tion, which we (hall find to be in the Forepart of the Cap-

fule of the Cryflalline Lens, about one-twentieth of an inch

from its outer edge : The Internal Layer adheres firmly to

the Vitreous Humour, till this is connected with the poflerior
part of the Capfule of the Lens, at the like diflance, nearly,
of one-twentieth of an inch from its outer edge ; and at the
diflance, therefore, of one-tenth of an inch from the con-
nexion of its Anterior Layer and Retina with the Lens.
The outer edge, therefore, of the Cryflalline Lens, covered
with its proper Capfule only, occupies a fpace nearly one-
tenth of an inch in breadth, between the two Layers of the
Capfule of the Vitreous Humour.

The Anterior Layer of the Vitreous Humour being fixed to
the Cryflalline Lens, at the diflance, nearly, of one-tenth
of an inch from the attachment of its Poflerior Layer, — ■
a Canal, bounded by the Two Layers of the Vitreous Hu-
mour, and by the edge of the Cryflalline Lens, as its balls,
is formed, which was difcovered by Dr Petit, and is named
after him *. Air, blown into this fpace, paffes, of courfe,

around

* Mem. de I’Acad. des Sciences, 1726,

OF THE CAPSULE OF THE VITREOUS HUMOUR, 81

around the Cryftaliine Lens. Each of the Two Layers of
the Capfule of the Vitreous Humour, is tougher than the
pofterior part of the Capfule, and adheres firmly to the Cap-
fule of the Lens

CHAP,

* See Table I. Fig. 3. 4. 5.

CHAP. II.

Of the Cryftalline Lens*

SECT. i.

Of the Capfule of the Cryjlalline Lens .

i I ''HE Capfule of the Cryftalline Lens, is of conftderable
thicknefs but has little toughnefs, or is eaftly cut or
lacerated.

The Capfule of the Vitreous Humour, by its divifion into
the Two Layers I have defcribed, has been fuppofed to form
it But this is an erroneous opinion ; for, it is not only

much

* Winslow, Traite de la Tete, 235. “ La Capfule Cryftallaine eft formee

par la Duplicature de la Tunique Vitre'e, comme j’ ai dit, 229.”

§4

OF THE CRYSTALLINE LENS.

much Thicker than the Capfule of the Vitreous Humour, but
is found on the Outer Edge of the Lens, covering that part
of it which lies between the Anterior and Pofterior Layers
of the Vitreous Capfule, and which is not covered by
thefe.

Oculifts, founding on the Divifion of the Capfule of the
Vitreous Humour into Two Layers, which pafs to the fore
and back parts of the Capfule of the Lens, have conlidered
thefe as Membranes fuperadded, and loofely connected to the
Capfule of the Lens ; and therefore pretend to detach the
Lens, in its proper Capfule, from the Pofterior Layer of the
Capfule of the Vitreous Humour, without lacerating it, or
breaking the Subfiance of the Vitreous Humour *. But, in
faft, Both Layers of the Capfule of the Vitreous LIumour
are fo intimately connected to, and incorporated with, the
Capfule of the Lens, that the Pofterior Part of the Capfule
of the Lens cannot be feparated from that of the Vitreous
LIumour, without tearing it, and, with it, the Subfiance of
the Vitreous Humour.

•

SECT.

* Mr. da Wenzel, on the Catarad, Sed. xxvi.

OF THE CRYSTALLINE LENS.

SECT. II.

Of the Structure of the Body of the Cryjlalline Lens, and Whether

the Fibres which enter into its compofition are Mufcular P

It has been long known, that the Cryftalline Lens confifts
of Lamellae, which are very foft and tender on its furface,
but become firmer, tougher, and heavier, as we approach
to its centre ; and that the Lamellae are compofed of
Fibres.

Leeuwenhoek, who firft obferved the Fibrous Structure
of the Lens, has defcribed them as difpofed in a very com-
plex and regular manner, and he fuppofed them to be Muf-
cular ; and this defcription and opinion have of late been
revived.

I had, many years ago, examined and demondrated the
Fibrous Stru&ure of the Lens, in the different dalles of
Animals, which I mentioned in my Book on Fillies, Ch. XI. 5
and, lately, I have repeated my obfervations, with the aid
of the Microfcope, without finding that the Fibres are dif-

L pofed '

OF THE CRYSTALLINE LENS.

pofed in the regular manner which has been defcribed and
delineated with fo much feeming accuracy, or that they can
be at all been till after the Lens is torn or cut : and, be-

lides their Want of Refeinblance to Mufcle and Tendon, the
following arguments appear to me to render the opinion of
their being Mufcular extremely queftionable.

1. After the Crydalline Lens is extracted, the Eye, affill-

ed by a Common Lens, feems capable of adapting itfelf to
different diliances. In Two Cafes I examined, above twenty
years ago, it appeared to be fo : At the fame time, I mud

acknowledge I could not trull fo entirely to the report of
the patients as to be fully convinced of this.

2. I fhall, in a following part of this Paper, endeavour to
prove, that we polfefs other means of accommodating the
Eye to objeds placed at different diflances.

3. The External Lamellae of the Lens, and the Matter
which connects the Lens with its Capfule, are fo extremely
Soft, that fuch a degree of mufcular a&ion of thefe Fibres
as could occalion any alteration of its general fhape, could
fcarcely fail to lacerate the external part of the Lens, and
to detach it from its Capfule.

4. In

OF THE CRYSTALLINE LENS.

4. In Fifties, where thefe Fibres are more manifeft than
in other Animals, as the Cryftalline Lens is nearly fpherical,
and the Matter compofing it nearly incompreflible, the Fibres
compofing its Lamellae, although they poffefied a Mufcular
Power, could neither change its Spherical Figure, nor render
it more Convex by leflening the Diameter or Bulk of the
Sphere.

SECT. III.

Of the Refractive Power of the Cryjlalline Lens.

It has been very generally fuppofed, by Anatomifts and by
Opticians, that the Refractive Power of the Cryftalline Lens,
compared with that of Water, is proportioned nearly to its
denfity 5 or, that its power exceeds that of WTater fomewhat,
on account of the Inflammable Matter which enters into its
compofition But different confiderations, and particular-

• L 2 ly,

* Haller, in Elem. Phyf. Vol. v. Lib. xvi. p. 402. “ Parvam eiTe qua aquam

f‘ fuperat, prseiogadvam, nuperi fatentur. Erit tamen aliqua, et ex ponderis ra*

“ done,

OF THE CRYSTALLINE LENS.

ly, that the rays of light cannot be refradted on entering
the Cornea in Fifhes, and therefore that their Cryftalline
Lens, which is not more diftant from the Retina than in
Land Animals, mu ft poflefs much greater power of Refrac-
tion, — having led me to fufpedt an error in the common
opinion, and to put this highly curious point of Phyfiology
to the teft of experiment, I difcovered, That the SjDherical
Nucleus of the Cryftalline Lens of the Cod, which, in fpe-
cific gravity, is to Water nearly as 6 to 5, and to common
white Glafs as 3 only to to, colleds the Light fo much
more powerfully than Water or Glafs does, that its Focus
is not more than one-fixth part of its Diameter diftant from
its Surface ; whereas the Focus of the Rays collected by a
Glafs Sphere, is at the diftance of one-fourth of the Dia-
meter of the Sphere ; and the Focus of the Rays colleded

“ tione, quae tamen fere fit ut u ad io, et particularum inflammabilium. An-

“ gulum incidentias radii ex humore aqueo in lentem venientis, ad angulum re-

“ fradtionis, facit uti 87 ad 85, cl. Porterfield : Eandem rationem seftimat

“ cl Pembertonus, uti 13 ad 12; et uti 21 ad 20, cl. Wintringham.” And

Dr Porterfield adds, “ This is a furprifingly fmall refradtion, and yet it is as
“ certain as any thing in Euclid, that it can be no greater.”

OF THE CRYSTALLINE LENS,

by a Sphere of Water, is diftant from it one-half of its
Diameter *.

On performing a fimilar experiment with the Human Cry-
ftalline Lens, I found, that the Focus, of parallel rays of
light falling on it, is at the diftance of three-eighths of an
inch from its Centre.

But, although this fhews, that its powers are far inferior
to thofe of the Lens of the Fifh, and even to thofe of Glafs,
which, of the fame fize and fhape, would colled; the light at

the diftance of a quarter of an inchf; yet, as the Specific

Weight of the Human Lens does not exceed that of Water
above a tenth part, its powers are much greater than have
been fuppofed by Authors j and the Focus formed by the
Human Lens, will be found to be fituated, nearly, half-way
between thofe produced by Glafs and Water.

CHAP,

* For a more particular Account of my Experiments, I fhall refer to my Book
on the Stru&ure and Fhyfiology of Fifties, 1785, — Chap. xi.

t In this calculation, I fuppofe that the Radius of the Sphere of which the An-
terior Part of the Lens is a portion, is 7f lines in length, and that of its Poftericr
Part 5 lines only.

/ '

CHAP. Ill

Of the Optic Nerves and Retina.

ir|HHE Optic Nerves have, in their whole courfe, lefs ap~
pearance of a Fibrous Stru&ure than perhaps any other
pair of Nerves in the Human Body.

SECT. L

FIence, although it appears to me evident, that the Me-
dullary Matter of the Right Nerve is incorporated with that
of the Left, where they are connected within the Head, yet
1 have found it very difficult, if not impoffible, to determine

ini

OF THE OPTIC NERVES AND RETINA.

in what proportion of parts the mixture is made, or to trace
either of the Nerves, with certainty, from its Origin to its
Termination in the Retina.

SECT. II.

Mariotte, above a century ago, has, by an ingenious ex-

periment, proved, that we are infenhble of an objed if its
pidure falls on the Entrance of the Optic Nerve into the
Eyeball. On repeating this experiment, many years ago, I
found, that the Diameter of the Objed which difappears is
very nearly equal to one-ninth part of our diftance from it j
or, that, at the diftance of Nine Feet from a wall, a Circle
One Foot in Diameter is loft. If, therefore, we fuppofe the
Human Eye to be One Inch or Twelve Lines in Diameter,
and that the Rays of Light, iftuing from the Objed, decuf-
fate about the Centre of the Cryftalline Lens, which is near-
ly Three Lines behind the Cornea, or Nine Lines from the
Retina, — the infenfible Spot on the Bottom of the Eye will
be One Line in Diameter ; and with this calculation I
found that the adual meafurement of the Medullary Part
of the Optic Nerve agrees very nearly.

OF THE OPTIC NERVES AND RETINA.

I next found, that an objedl begins to difappear, when the
point to which the Eye is directed, is One-fourth of the di-
ftance of the Eye from it ; and hence, upon the fuppohtion
above Rated, the Axis of the Eyeball will be found to be
Two Lines and a Quarter from the Outer Side of the Op-
tic Nerve, and Two Lines and Three Quarters from its
Centre.

SECT. III.

When the Nerves, after entering the Eyeballs, form the
Retina, their Colour is changed from White to Cineritious ;
but no Fibres are to be feen in the Human Retina, even
with the Microfcope ; but the whole appears to be com-
pofed of an Uniform Pulpy Matter, on the Outer Side of
which, chiefly, Veffels are difperfed, fupported, as I fuppofe,
by a Membrane the fame with or analogous to the Pia
Mater. The term Retina is therefore improper, where it is
applied to exprefs a Network or Fibrous Texture.

SECT.

OF THE OPTIC NERVES AND RETINA.

SECT. IV.

Of the 'Termination of the Retina.

Not long after I began to Rudy Anatomy, finding very
contradidtoy accounts of the Termination of the Retina,
given by the moR eminent Authors *, and even by the fame

Authors,

'* Winslow, Traite de la Tete, 237.: “ C’eft peut-etre cette continuation

“ qui fait quelquefois paroitre les Feuillets ou Procefies Ciliaires com me revetus
“ d’une Pellicule Blanchatre ; et c’efl: peut-etre, auffi, ce qui augmente l’epaifieur
« de la portion anterieure de la Capfule Cryftallaine.” Yet, in p. 231. he de-
fcribes the Black Paint of the Choroid Coat as connected with the Capfule of the
Vitreous Humour, inftead of the Retina : “ Les Sillons Rayonne's de la Tunique

<4 Vitree font tout a fait Noirs.”

Haller, Pr. Lin. dxv. : “ Ubi vero Retina ad Procefius Ciliares pervenit,

“ feauitur eorum duclum, et ad Lentem properat, in hujus Capfulam innata, et
11 huic obdudta, fi fides et aliorum cl. Virorum et meis experimentis haberi poteft :
“ neque enim de eo fine in Quadrupedibus conftat.” But, in a later Work, he
expreffes his doubts of the accuracy of the above defcription : El. Phyf. Lib. xvi.

p. 388. “ Omnibus perpenfis, amplio, ei fententiae propior quae Membranulam a

‘s Retina diverfam, inter Uveam et Vitream, ad Lentem producit.”

OF THE OPTIC NERVES AND RETINA.

Authors, as Drs Haller and Winslow, I examined this
matter with fome care in the Human Eye ; and it then ap-
peared to me, that the Retina terminated abruptly about the
Root of the Ciliary Procefles, refembling the Brim of a Tea-
Cup : And, as the opinion of Winslow, Ferrein, and, at

that time, of Dr Haller, that it was fixed to and covreied
the Cryflalline Lens, appeared to me incredible, becaufe it
would have been flruck with the Light, before this was col-
lected into a Focus or Picture ; and as a Figure, publiihed,
fome time thereafter, by the generally accurate Zinn* **, feemed
to correfpond with what I had feen, I profecuted the fub-
jeCt with lefs attention than perhaps I fhould otherwife have
done.

Lately, I afked the favour of my very dexterous and ac-
curate Alliftant, Mr Fyfe, to repeat the duTeCtion of the
Eye, in the Ox as well as in the Human Body, and to draw
-a Figure of the Termination of the Retina. His fir ft Figure

M 2 correfponded

* Zinn, Tab. ii. Fig. i. and in Cap. iii. p. u 6. lin. 13. “ Ad Originem
tl Procefluum Ciliarium, non fenfim evanefcere, led Fine ubique requali et ac-

** curate limitato terminari.”

OF THE OPTIC NERVES AND RETINA.

correfponded with what I had obferved : But he told me,,

afterwards, That, on being ftill more cautious in his di flec-
tion, the Retina appeared to him to be continued on tlie-
Inner Side of the Ciliary Procefles, and to terminate in the
Outer Edge of the Cryflalline Lens. On reviewing the
fubjed:, I obferved, beyond all doubt, that this is the cafe ^
and likewife difcovered the caufes of the error into which
I had fallen with Dr Zinn. In the firfl: place, When the
Continuation of the Choroid Coat and Ciliary Procefles is
lifted up, the Black Paint, which lines thefe, adheres to and
conceals the Retina. In the next place, The Retina has fo
much fupport from the Paint on its Outer Side, and fitch a
degree of Adhehon, firfl; to the Capfule of the Vitreous Hu-
mour, and then to the Edge of the Lens, and has fo little
Connedion to the Choroid Coat behind the Root of the Ci-
liary Procefles, that, in the courfe of the diflection, a flight
Prefiure being made, the Retina is lacerated, and appears to
terminate abruptly at the Root of the Ciliary Procefles.

To fhew the Termination of the Retina in the Outer
Edge of the Cryflalline Lens, let the Eye be laid on the
Cornea, and a Circular Cut then made, through all the Coats
of the Eye and Vitreous Humour, behind the Ciliary Circle ;

the

OF THE OPTIC NERVES AND RETINA.

the Retina will then be feen, lining the Black Paint upon
the Ciliary Proceffes, and palling from thefe to the Lens.

Next, let the Cornea and Sclerotic be taken off, the Iris
cut away, and the Ciliary Proceffes raifed off from the Paint
which lines them and flicks to the Anterior Part of the Re-
tina ; and then, with a very foft Pencil, dipt in water, let
the Black Paint be brufhed off, and the whole Courfe of the
Retina will be feen diftindly.

On examining the Retina with rtill greater accuracy, it
appears, that it has exadly the fame Number of Folds or
Doublings that the Choroid Coat has for it enters Double
between the Ciliary Proceffes, nearly in the fame way that
the Pia Mater enters into the Furrows of the Brain. The
Furrows and Doublings of the Retina, which, if we are to
ufe the favourite term of Ciliary , may be called its Ciliary
Proceffes, make an impreffion on the Anterior Part of the
Vitreous Humour*

I have already obferved, that the Black' Paint lining the
Ciliary Proceffes of the Choroid Coat, has a confiderable ad-
hefion to the Retina, which Is Thinner here than on the
Pofterior Part of the Vitreous Humour- 5 and, on its Inner

Side,,,

♦

OF THE OPTIC NERVES AND RETINA.

Side, the Retina adheres dill more firmly to the Coat of the
Vitreous Humour, which is much Tougher here than it is
where it covers the Back Part of the Vitreous Humour.
At laft, the Extremities of its Ciliary ProceiTes divide into
a ft ill greater Number of Parts or Fibres, refembling the
fmall Branches of Nerves in other places of the Body, which
are clofely connected to the Fore Part of the Capfule of
the Lens, about One-twentieth of an Inch diftant from its
Outer Edge, or Place where the Anterior and Pofierior
Plano-convex Lenfes which form it, are joined together.
After which, thefe Fibres either terminate, or become fud-
denly fo pellucid, that it is impoffible to trace them farther ;
and it is furely highly improbable that they form an Exter-
nal Coat to the Capfule of the Lens, as Winslow, Ferrein,
and Haller, fuppofed, or that their Continuation on it af-
fifis in Villon, as the Rays of Light are not fo fully col-
lected upon the Capfule of the Lens as to form a difiinCt
Picture, and we farther obferve, that when a CataraCt is
very opake, the Light which falls on the Capfule of the
Lens gives no diltinct idea of objects.

The Retina, at its connection with the Vitreous Humour
and Cryftalline, is remarkably Tougher than it is in any other
part ; or it feems to adhere there, to the Anterior Layer of

the

OF THE OPTIC NERVES AND RETINA.

the Capfule of the Vitreous Humour, by Cellular Threads,
or perhaps by the Pia Mater, which, as I have elfewhere en-
deavoured to prove, accompanies the Nerves in their whole
progrefs.

In the feveral Figures of Table Firfl, and Table Firft
the Courfe and Termination of the Retina are accurately
reprefented ; and the Reader may now confult the Expla-
nation given of thefe Tables.

In confequence of the Termination of the Retina being"
extended to the Cryfcalline Lens, it is evident, that, in
Couching, the Surgeon mult, before he reaches the Lens,
wound the Retina with his Needle ; and if he afterwards
deprelfes the Capfule along with the Body of the Lens, or
if a Needle is palled around the Lens in order to detach it
from the neighbouring parts, as has been advifed f, the
Anterior Edge of the Retina mult be lacerated, and very
much injured.

f Mr. da Wenzel junior, on the Cataraft, Sect. xvi.

ICO

OF THE OPTIC NERVES AND RETINA.

As the Rays of Light cannot be diredtly colledted, fo as
to form a diftindt Pidture on that part of the Retina which
lines the Ciliary Circle and Ciliary ProcefTes, there is per-
haps reafon to fiifpedt, that the Light which is refledted
from the Pidture formed at the Bottom of the Eye, does not
aflift Vifion, by giving a Second Stroke to that part of the
Retina on which the diftindt Pidture is formed, — which feems
to be the idea of Authors ; for fuch a Second and Pofterior
Stroke would have nearly or exadtly the fame effedt as the
Firft : But rather, that we receive, on the Anterior Part of
the Retina, lining the Ciliary Circle and Roots of the
Ciliary ProcefTes, a Second and very different kind of Im-
pulfe, by the Light refledted from the Bottom of the Eye
to this part, by which we fee and judge better of the
objedt.

This fuppofition feems to be ftrongly fupported by the
general obfervation, that the Paint lining the Choroid Coat
at the Bottom of the Eye, which has been called Tapetum ,
is remarkably Bright, and fit for the Refledlion of Light in
thofe Animals which feek their food in the Night-time, when
fuch an aid is evidently molt necefiary.

The

OF THE OPTIC NERVES AND RETINA.

IOI

The Analogy of the Cochlea of the Ear, which receives
One Impulfe through the Chain of Bones connedted to the
Membrane of the Oval Hole, and Another by the Membrane
of the Foramen Rotundum, fupports this Opinion.

CHAP,

CHAP. IV.

Of the Choroid Coat and Ciliary Procefles.

TN Man, and, fo far as I have obferved, in all the Genera of
the Mammalia, Birds, Amphibia, and Fifties, the Choroid
Coat and Ciliary Procefles conflft of a Vafcular Coat lined with
Paint : But, in one Species , the White Rabbit, I have found,

that the Paint is wanting *, and the fame thing is true of
their Iris ; and hence their Eyes appear Red ; becaufe the
Blood circulating in the Vafcular Part of the Choroid, is feen
through the Humours. It is probable, that in other Species
or Varieties of Animals in which the Eyes appear very Red3
a flmilar Defed of the Paint will be difcovered,

N 2 I

* Book on Filhes, Chap. xii.

104

OF THE CHOROID COAT

I have already obferved, that the Colour of the Paint is
Brighteft, and moft fit to refled Light, in thofe Animals
which feek their food in the Night-time : But, in all Ani-

mals which have the Paint, it is found to be Black where
it lines the Ciliary Circle and Proceffes, or where it covers
the Anterior Part and Termination of the Retina; in order,
I fuppofe, to fuffocate the Rays of Light which are refleded
from the Bottom of the Eye upon this part of the Retina :
And this feems likewife to confirm what I have alleged,
that no advantage in Vifion is to be derived from Light
ftriking firft the Inner- fide, and then being refleded upon
the Outer-fide of the fame part of the Retina.

When the Paint is carefully wafhed off from the Inner-
lide of the Choroid Coat, we fee evidently, that the Ciliary
Precedes are formed by the Continuation of the Choroid
Coat, folded feventy or eighty times, fo as to occupy a
fmaller Circle.

The Ciliary Circle, and Roots of the Ciliary Procefles,
are firmly glued to the Anterior Part of the Retina, almoft
as far as to its Termination, or Infertion in the Outer Edge
of the Lens : But the Points or Terminations of the Ciliary

Proceffes float loofe in the Pofterior Chamber of the Aqueous

Humour,

*»

AND CILIARY PROCESSES.

105

Humour, and have no diredl Connexion with the Lens,
Zinn, who obferved that the Terminations of the Ciliary
Procedes were not connected with the Lens concluded
therefore, that the Inner Parts of the Ciliary Precedes were
inferred into the Capfule of the Vitreous Humour f : But

I have already obferved, that the Anterior Part of the Retina
reaches to the Edge of the Lens, or intervenes between the
Ciliary Procedes and Vitreous Humour.

It appears therefore, That the Ciliary Precedes do not
form a complete Septum between the Aqueous and Vitreous
Humours ; and, That the Capfule of the Cryflalline Lens is
not fupported in its place by the Terminations of the Ciliary
Procedes of the Choroid Coat in it ; but that it owes its
Support to the intimate Union of its Poderior Part with the
Poderior Layer of the Capfule of the Vitreous Humour, and

* See Zinn, Chap. ii. p. 66. “ Ipfa tamen ilia extrema libera, ad Lentem

“ non folum pertingant, fed etiam ultra ejus Circulum maximum progrelTa, See.
“ fine pendulo libero, &.c. terminantur.”

t Zinn, Chap, ii, p. 78, “ Vitreo ardlilTime funt junfti.”

106 OF THE CHOROID COAT, &c.

to the Infertion of the Anterior Layer of the Capfule of the
Vitreous Humour and Retina into it, near to its Circum-
ference.

Whilft the Retina, by the Toughnefs of its Pia Mater,
gives more additional Support to the Lens than we might
be apt to fuppofe from its general Tendernefs ; it is itfelf
fupported in its place, befides ferving the ufe before men-
tioned, of receiving Imprellions by the Light refleded from
the Bottom of the Eye.

In the feveral Figures of Table Firffc, and Table Firft
tliefe Parts are delineated j and to the Explanation of them
I lhall refer the Reader.

CHAP.

CHAP. V.

Of the Iris.

SECT. I.

TN the Book I publilhed on Fifties I Bated the feveral
circumftances which prove, beyond doubt, that the Veflels
of the Iris are not Colourlefs, as Ruysch, Vieussens, Fer-
rein, Dr Haller, Zinn, and others, following them f , have

taught 5

* Chap. xi.

f Ruysch, Ep. xiii. — Vieussens, Tr. de Lin. p. an. — Ferrein, Mem. de
l’Acad. (1739). — Haller, El. Phjf. Lib. xvi. Se£t. ii. § xxxiii. p.435. “ Ex
“ eo porro Circulo numerofa Vafcula in Uveam veniunt, in variis Animalibus,

“ et

io8

OF THE IRIS.

taught , but that, on the contrary, they are Large, Red,
Numerous, and circulate an extraordinary quantity of Red
Blood.

Since that time, I have obferved, in one cafe, a White
Speck on the Iris, produced by Inflammation, on the Sur-
face of which I could fee diflindly Veflels filled with Red
Blood.

In three other cafes, I have obferved a very remarkable
appearance, which, fo far as I know, has efcaped the obfer-
vation of Oculifts.

In two of thefe cafes, where the Eyes had been long in-
flamed, a Network of Filaments palled from one fi.de of the
Iris, acrofs the Pupil, to the other fide of it, covered with
Paint of the fame colour with that of the Iris.

“ et imprimis in Pifcibus, Sanguine plena, in Homine pellucida.” — Zinn de Oculo,
Cap. ii. p. 92. Not. f. “ Ut inde elici pofle videatur in Homine vivo, VaCcula
“ liquorem fanguine tenuiorem et decolorem vekere.”

OF THE IRIS,

109

In the third cafe, of a Perfon who had had a White Ca-
taract in one of his Eyes for upwards of Twenty Years, a
Network of Veflels, covered with Paint darker than that of
the Iris, was extended from the Iris upon the Surface of the
CataraCt.

I pointed out thefe appearances, in one of the cafes, to
Mr Anderson, Surgeon in Leith, and, in another, to Mr
Law, Surgeon in Edinburgh, who were attending the Patients
along with me.

SECT. II.

The Nerves of the Iris are fo numerous, that, proportioned
to its Weight, no part of the Human Body is perhaps fo plen-
tifully fupplied with them.

SECT.

OF THE IRIS.

SECT. III.

But, what account are we to give of its Mufcular Fibres >
or of thofe Fibres by means of which its motions are per-
formed ?

When we look into the Works of Dr Haller, we find
this celebrated Author, after quoting the accounts given by
others, affirming, in the moft pointed manner, ’ That, although
he examined the Iris of the Ox with the Microfcope, he
could not perceive in it any Circular Fibres : And his Pupil

and Succeffor (Dr Wrisberg) affirms the fame

Confiding

* Haller. El. Pliyf. Lib. xvi. Se£t. n. p. 371. “ Ex hypothefi, plurimi

44 Scriptores Fibras effe, in circulum circumdu&as. Verum eas iaepe, et myopibus
44 meis, caetera bonis, oculis, et lentibus vitreis, vehementer augentibus, adjutis
54 cum quaererem, nunquam reperi ullas.” — p. 378. 44 Circulus in Uvea conftri&or

14 nullus eft.”— —Haller. Pr. Lin. Phyf. § dxii. 44 Qrbiculares Fibras, con-

centricas

OF THE IRIS.

Confiding in the accuracy of Dr Hal£er, I, for many
years, examined this organ with lefs attention than, probably,
I fhould otherwife have done. But having, at laft, examined
carefully the Iris of an Ox, after wafhing off the Paint, I
was not more pleafed than furprifed, to find, on its Anterior
Part, a broad flat oval Organ, with Fibres of a dark reddifh
Colour, difpofed in nearly the fame manner as thofe of the
Orbicularis Palpebrarum are.

Its appearance is, in all refpe&s, fo evidently Mufcular,
that I think there can be no doubt of its being the iphinfler
of the Pupil : And I can only account for its having efca-

O 2 ped

“ centricas Pupillae, neque Oculus, neque Microfcopium, ne in Bove quidem, mihi
“ demonftravit.”

In a tranflation of Notes by Dr Wrisberg on Haller’s Primae Lineae, the
Dodtor writes as follows : “ Befides anatomical proofs, by which it is undoubted-

“ ly certain, that the Iris has no real Mufcular Fibres, and that the contradtion and
“ dilatation of the Pupil is rather to be afcribed to the Veffels than to Mufcles.”

Zinn de Oculo, Cap. ii. Seel. iii. § iv. p. 91. “ Dubius certe haereo, annoa

“ Fabrica Mufculofa in Iride agnofeenda efie videtur.’J

212

OF THE IRIS.

ped the obfervation of Dr Haller and Dr Wrisberg, by
fuppofing, that they had not waihed off the Black Paint,
which covers and conceals it, as well as the Red Veffels of
the Iris.

On the Inner and Anterior Part of the Iris, and on the
whole of its Pofterior Part, the Fibres are difpofed like Ra-
dii and, if they are Mufcular, they are well fituated for
dilating the Pupil. But thefe have many more Blood-veflels
in their compolition, and have much lefs the appearance of
Mufcular Fibres, than the oval fibrous Organ I have defcri-
bed on the Forepart of the Iris.

In Table II. Fig. i. and 2. thefe Parts are elegantly and
accurately reprefented, from Drawings made of them, at my
requeff, by Mr Fyfe.

My fuccefs in the Ox naturally prompted me to examine
the Human Iris with greater attention than I had formerly
bellowed on it ; and in this I found, with equal fatisfadion,
a very diftind Sphinder Mufcle ; but fomewhat differently
difpofed ; for in Man it occupies the Innermoft Part of the
Iris, or forms a Ring immediately furrounding the Pupil,
which is equally well feen on its Fore and Back Parts, and

makes

OF THE IRIS.

i*3

makes about One-Fifth Part of the Breadth of the Iris.
Between the Sphin&er and Root of the Iris, the Space is
filled up with Vehels and Radiated Fibres.

See Table III. and its Explanation.

Dr Zinn, Dr Haller, and Dr Wrisberg particularly,
the two latter, have doubted of, or denied, the Mufcular, or,
as they fpeak, Irritable nature of the Iris ; becaufe the Con-
traction of the Pupil is not occasioned by Strong Light fall-
ing upon it.

But

* Zinn de Ocufo, Cap. ii. Sect. in. § iv. p. 95.

Haller. El. Phyf. Lib. xvi. Se6t.il. p.371. u Nam, per experiments folicite
ie capta, Iris in vivo animate Irritabilitate omni deftituitur, ipfisque a lucis radiis, .
“ per conum chartaceam in folam Iridem determinatis, non movetur ; fed Muf-
“ culo proprium eft, effe irritabilem.’*

Wrisberg, in a Note on Haller, Pr. Lin. Phyf. § dxiii. “ My own ex-
“ periments have convinced me, that the Iris does not belong to the parts en~
u dowed with regular Irritability; for the folar. light dire&ed upon the Iris re-
“ mains without any fuch effetV5

OF THE IRIS.

l.i 4

But their inference is by no means to be admitted.

Becaufe, without alleging that its being roufed into adtion
by the irritation of the Retina, is fcarcely to be ex-
plained, but on the fuppofition that the Living Princi-
ple is firft excited, and a Mufcular Adtion in confequence
produced ; I would obferve, that the Colour or Paint upon
the Iris, which prevents the Light from getting to the Bot-
tom of the Eye except through the Pupil, muft, like a Cuti-
cula, prevent the Light from irritating the Iris, unlefs we
fuppofe it to be concentrated in a very great degree.

In the next place, we are to confider, that, in the com-
mon offices of life, Light is colledted into a Focus, or fo
concentrated, that it may prove hurtful to the Retina alone ;
and therefore Nature has, in general, regulated the adtion of
the Iris, according to the Quantity of the Light which falls
upon the Retina.

I would further obferve, that various other Mufcles are
thrown into a more fudden and violent adlion, by Stimuli
applied to diffant organs, than if the fame Stimuli had been
diredtly applied to thofe Mufcles. Thus, if a Drop of Cold
Water, or even a Drop of Warm Saliva, falls into the Glot-
tis,

OF THE IRIS.

tis, the very diftant Abdominal Mufcles are fuddenly con-
vulfed. I furely need not fay, that the Warm Saliva, di-
rectly applied to thofe Mufcles, laid bare by diffeCtion, would
produce no fuch effeCt.

In the laft place, I have, many years ago, obferved in the
Parrot, that the Pupil is, alternately, greatly contracted and
dilated, whilft the Eye is expofed to the fame degree of
faint Light * ; which is quite inconiiltent with the idea,
that the aCtion of the Iris is produced by the foie and di-
rect effeCt of Stimuli applied to it.

CHAP.

See Dr Porterfield’s Book on the Eyes, Vol. ii. Chap. v. p. 151.

CHAP. VI

Of the Veflels of the Cornea.

SECT. i.

TN the Book which I publiflied on the Strudure and Phy~-
“*■ flology of Fifli.es, in the year 1785, I obferved, (Ch. XL)
that the Veflels containing Red Blood, which are been upon
the Cornea after an Inflammation of it, are not its original
Veflels dilated, but are newly-formed Veflels, rooted in the
Tunica Adnata, and extended, from it, oyer the External
Surface of the Cornea } and hence, that Surgeons might per-
ceive the propriety of attempting to remove thefe, and the
Specks produced by them, by Chirurgical means and Exter-
nal applications.

I would

z 1 8

OF THE VESSELS OF THE CORNEA.

I would now obferve, that, in every cafe I have examined
fince that time, I have found a confirmation of the truth of
the above alTertiom

SECT. II.

It may be worth while to add, that, on examining an
Opake Circle, which, in many very old Perfons, encroaches
upon the Cornea, I have found that Circle full of very mi-
nute Veifels, rooted likewife in the Adnata, and extended on
the External Surface of the Cornea, without entering between
its Layers.

CHAP.

CHAP. VII.

Of certain Laws by which we judge of
the Pofition and Distance of Objects,
and by which we regulate the Motions
of the Eyes.

SECT. I.

A LT HOUGH the whole PiUure of an Object formed
on the Bottom of the Eye be inverted, we form a juft
judgment of the Pofition of its Parts becaufe we are taught
by Iiiftindt, that each Pencil of Rays which firikes the Re-
tina mutt have come from the oppofite fide. Juft as, when
our Hand is held fupine in the horizontal pofture, if the

P Back

i2o LAWS BY WHICH WE JUDGE OF THE

Back of it be ftruck, we fuppofe the Broke to have come
from Below j and, if the Palm, from Above.

I apprehend we are further taught by Inftindt, that the
Tight has palled through the Pupil, and that we therefore
form a more correct idea of the Polition of the Objetfl,
than when, with Authors *, we imagine, that the Light is
traced perpendicularly from the Place of the Pi&ure.

SECT. II.

As we derive many advantages from directing the Axes
of the Two Eyes to the fame point, the fuppoftion made by
Authors, that this Direction is not given by Inflinct, but

proceeds

* Dr Porterfield and Dr Reid. See Dr Reid’s Inquiry into the Human

Mind, On Seeing, Chap. vi. Se£t. xii. p. 261. “A vifible object appears in the
“ direction of a right line, j perpendicular to the retina at that point where its
“ image is painted.”

POSITION AND DISTANCE OF OBJECTS.

121

proceeds from Cuftom and Habit *, mud, at firft fight, ap-
pear extremely improbable ; and the more I have attended
to the Motions of the Eyes, not only in Infants, but in other
very young Animals, the more I am convinced that the Uni-
form Motion of the Eyes, and the^ accurate Direction of Both
to One Point, is Original.

We may obferve many other Complex Actions, Refpiration,
Sucking, Deglutition, performed without Experience : Why

then doubt that the Uniform Motion of the Eyes is regulated
by a limilar Law ?

That, by Habit, we are lefs able to move the Eyes in
different Diredions in the advanced than in the early period
of life, is at the fame time true.

SEC 1’.

* Dr Porterfield on the Eye, Vol. I. Book ii. Chap. v. p. 23. “ The true
“ caufe of this uniform motion depends on Cuftom and Habit.”

Dr Reid, p. 240. “ Nature hath very wifely left us the power of varying
“ the parallelifm of our Eyes a little, fo that we can direft them to the fame
“ point, whether remote or near. This no doubt is learned by Cuftom.”

1 22

LAWS BY WHICH WE JUDGE OF THE

SECT. III.

The Diredion of the Optic Axes furnifhes, no doubt, an-
auxiliary means by which we judge of the Didances of Ob-
jects ; but drange overfights have been committed by Au-
thors on this fubjed, and particularly by Dr Porterfield,
who fuppofes effects to proceed folely from this caufe, which
evidently flow from others.

Thus, he tells us, that when a Perion has had the mis-
fortune of lofing one of his Eyes, or even if a Perfon
fhuts one of his Eyes, he cannot readily fill out a difli
of tea, or fnuff a candle, becaufe he wants the concurrence
of the Optic Axes ; without confidering, that the degree
of adion or draining of the Mufcles neceflary to dired
the Axis of One Eye to the objed, would have nearly the
fame elfed on tiie Mind as the Diredion of Both Axes to
the fame point. Befides, he forgets, that the Axis of the
Eye which is fliut, and even that of the blind Eye, for a
long time at lead, follows the motion of the other.

POSITION AND DISTANCE OF OBJECTS.

123

In like manner, in his principal experiment by which he
proves that the Eyes accommodate themfelves to the Di fian-
ces of Objeds, he obferves, that if we fhut the Left Eye,
and, with the Right Eye, view a Luminous Point through
two fmall Holes in a Card, this Point will appear Single at
a certain diftance to which the Eye is accommodated, but
will appear Double in all other fituations ; becaufe the Rays
of Light which pafs through fmall Holes, form fuch diftinCt
Pictures, that the Eye is not folicited to alter its Conform-
ation to the Diftance. And he proves that the above is a
juft account, by next obferving, that if the Left Eye is open-
ed, and Both Eyes directed to the Luminous Point, the Dou-
ble appearance of it inftantly vanifties. But, in attempting
to explain the Caufes which prompt the Mind to ad, he fup-
pofes, that the Two Optic Axes being now direded to the
fame Point, we are enabled to take the Angle, and fo meafure
the Diftance ; not refleding, that the Axis of the Left Eye,
whilft it was Shut, was guided by the Diredion of the Open
Eye, or had had the fame Diredion when it was Shut, as
when it was Opened.

Hence Dr Porterfield, though he proves, by this expe-
riment, that the Eye alters its Conformation, has not point-
ed

124

LAWS BY WHICH WE JUDGE, &c.

ed out the true Means by which it judges of the Diftance,
and is therefore folicited to aft.

Thefe, I apprehend, in this cafe, depend on the clearer
view which the Two Eyes receive, not only of the Lumi-
nous Point, but of the relative Situation of the feveral Ob-
jects which are nearer to or farther from us than it ; by
means of which the Mind judges more accurately of the
Diftance, and therefore accommodates the Eye to it.

G H A P.

CHAP. VIIL

Of the Means by which we accommodate
the Eye to the Diftances of Objects.

HjmHAT the Human Eye pofiefles the power of accommo-
A dating itfelf to the Diftances of Objects, feems beyond
a doubt * : And, I think, I can prove, that this power is

not reftri&ed within the narrow limit of Twenty-feven In-
ches, as Dr Porterfield contends j for I find, that when
I place two minute Obje&s in nearly the fame line, the
neareft of them at the diftance of Three Feet, and the other
at double or treble that diftance, on viewing them alternate-
ly with one Eye, they become alternately confufed and
diftinct.

But

•* See Dr Porterfield on the Eyes.

126

MEANS BY WHICH WE ACCOMMODATE

But, to afcertain the Means by which the Eye accommo-
dates itfelf to the Diftances of ObjeCts, is a matter of much
difficulty.

The following are the chief Means enumerated ; on each
of which I fhall make a few Remarks. And I ffiall then
point out an Additional Means, which has efcaped the ob-
fervation of Authors.

SECT. I.

It has been fuppofed, that the Fibres which enter into the
compofition of the Cryftalline Lens are Mufcular, and that,
by their Contraction, they render the Lens more Convex,
and therefore adapt the Eye to near ObjeCts. But to this
opinion I have, in the Firft Chapter of this Paper, propofed
Objections, to which I ffiall refer the Reader.

SECT.

THE EYE TO THE DISTANCES OF OBJECTS, 127

SECT. II.

The Ciliary Procefles have been fuppofed to be chief
agents. But, without Bating, that Mufcular Fibres are not
to be feen in thefe Procefles *, or the improbability that the
Choroid Coat, of which they are the Continuation, in the
form of Folds or Doublings, is Mufcular, as its general ac-
tion would be ufelefs and even injurious to the Retina ; and
without repeating the argument, that the Eye feems to ac-
commodate itfelf after the Extraction of the Lens ; — I would
remind the Reader, that their Extremities float loofe in the
x^queous Humour, and that their Inner-part is connected to
the Lens by the medium of the Retina : Nor is their direc-
tion fuch, that they can be fuppofed capable of pulling the
Lens forwards, by pulling the Retina : Or, if we were to

fiippofe them to be Mufcular, and to a<5t with confiderable
force, they would render the Lens flatter, by pulling its

0.2 Circular

* Zinn, Cap. ii. p. 70. “ Neque unquam -Microfcopio imicam Fibram Miifcu-

“ larein reperiri potm.”

128

MEANS BY' WHICH WE ACCOMMODATE

Circular Edge outwards, and would therefore have the effed,
contrary to what is fuppofed, of rendering the Eye lefs fit
for viewing near objeds.

SECT. III.

The Iris, by lellening the Pupil, and cutting off the moil
diverging rays of light, when we are viewing near objeds,
unquedionably makes the Pidure on the Retina more diflind,
and therefore renders the Objed more diftind.

SECT. IV.

Some, as Jurin, have thought, that the Iris might, by its
Contradion, have the effed of drawing the Root of the Cor-
nea inwards ; and, by this means, render the. Cornea more
Convex : And the Difpolition of the Sphinder Mufcle of

the Iris, efpecially in the Ox, may feem to fupport this
opinion.

But

THE EYE TO THE DISTANCES OF OBJECTS.

129

But I muft obferve, That the Iris is not Rooted in the
Cornea, as thofe who maintain this opinion fuppofe, but in
the Sclerotic Coat, which in Man is thicker and refills more
than the Cornea, and in many other Animals is remarkably
hard and inflexible. Befides this, I have fhewn, that, in
Man, the Sphincter Mufcle of the Iris is placed on the In-
ner Edge of the Iris, with the interpofition of the Radiated
Vafcular Subfiance between it and the Sclerotic ; fo that it
cannot directly affect the Sclerotic and Cornea.

To thefe we may add, that, in a clear light, when the
Iris is flrongly contracted, we fee remote objects diflinclly :
Whereas, if the flrong contraction of the Iris which then
takes place, rendered the Cornea more Convex, and thereby
fitted the Eye for near objects, thofe fhould appear con^
fufed.

SECT. Vo

The External Mufcles, and particularly the Recti, have,
by many, been thought to be well adapted for elongating
the Axis of the Eye and a late Writer alleges, that the

Recti.

MEANS BY WHICH WE ACCOMMODATE

Redi terminate partly in the External Layer of the Cornea,
and therefore are better fuited, than was imagined, for fuch
a purpofe. But here I would obferve, in the firfb place,
That, on re-examining this point of Anatomy with attention,
I have found all the Tendinous Fibres of the Redi firmly
attached to the Sclerotic, at the diflance of a quarter of an
inch from the Edge of the Cornea, and no appearance that
any part of them, or that any Membrane produced by them,
is continued over the Cornea*.

'* By experiment on the Human Eye, I found, that the Weight of Fifty-four
Ounces tore one of the Re£H Mufcles ; but that it required the Weight of a Hun-
dred Ounces to tear its Tendon from the Sclerotic Coat, and when the Tendon
quitted the Sclerotic, there was no appearance feen of its Fibres palling forwards

ever the Cornea. And, the generally very accurate, Zinn, who had no parti-

■

cular Theory to fupport or to refute, exprefles hkmfelf on this fubjedt in the fol-
lowing words : “ Tendines illorum Mufculorum linguli, etfi ad infertionem la-

41 tiores evadunt, dillinfti tamen femper manent, et, ubi immiffis in Scleroticam
e‘ Fibris, iili tarn intime jam affiguntur, ut line manifefta laceratione ulterius dividi
“ non pofiint, fatis magno inter fe diftant intervallo, nec alibi fefe contingunt, ut,
“ nunquam in unum jungi, aut propriam tunicam ccntinuam conflituere polTe, affir-
u mari poflit.” Zinn de Oculo, Cap. i, p. 14.

THE EYE TO THE DISTANCES OF OBJECTS.

131

In the next place, if they had terminated partly in the
External Layer of the Cornea, in fuch a manner as to af-
fect it chiefly, they fliould, by pulling the whole External
Layer of the Cornea backwards, have flattened the Cornea,
inftead of rendering it more convex.

SECT. VI,

About fifteen years ago, it occurred to me, that, although

we fliould grant, to Dr Porterfield and others, that the
Axis of the Eye could not be elongated by the Retfli Muf-
cles ; yet, that the Oblique Mufcles, which are thrown, in
oppofite dire&ions, around the Eyeball, might have this e fi-
fe ft. I have fince obferved, that Dr Keil, Hambergerus*
and other Phyfiologifts, had long ago entertained the fame
idea *,

* Dr Keil, Ang. Chap. iv. Se&. iv. “ The Aqueous Humour, being the
4‘ thinneft and molt liquid, eafiiy changes its figure, when either the Ligamentum

“ Ciliars..

132 MEANS BY WHICH WE ACCOMMODATE

To be better underflood, I had a Preparation and Draw-
ing made of the Oblique Mufcles ; from which Table III.
was engraved.

SECT. VII.

I shall conclude, by pointing out one other Means, that
had not occurred to Authors, which we employ when we
view minute obje&s placed near to the Eyes.

If we attend to what pafles in that cafe, we may be fen-
fible that we bring the Upper and Under Eyelids nearer to
each other; and then, by a confiderable exertion, contrad:
the parts about the Eyes.

u Ciliare contra&s, or both the Oblique Mufcles fqueeze the middle of the Bulb of
u the Eye, to render it oblong, when obje&s are too near us.” — ■ — - Briggs et
Hamberger. de Oculo, p. 180. propofe the fame opinion.

THE EYE TO THE DISTANCES OF OBJECTS. 133

On confidering this, it appeared to me probable, that the
Orbicular Mufcle of the Eyelids might, by its preflure on
the Upper and Under Parts of the Cornea, make thefe fome-
what Flatter, and, of courfe, protrude the Middle Part of
the Cornea between the Edges of the Eyelids, fo as to ren-
der it more Convex ; at the fame time increafing its di~
fiance from the Lens, and lengthening the Axis of the Eye-
ball.

On putting this matter to the tell of the following Expe-
riments, the event appeared to correfpond exa&ly with the
idea I had formed.

EXPERIMENT I.

In a clofet, lighted by a fingle window, I fat on a chair,
with my back to the window,^ and fixed a Book, with Small
Print, on the oppofite walk I then brought my Eyes fo
near to the Book, that the Letters became indiflindl. I
then made an Exertion to read, without contracting the Or-
bicularis } or, I opened the Eyelids wide, by adling with,

the Attollens Paipebram Superiorem 5 or, I held the Upper

R and.

1 34-

MEANS BY WHICH WE ACCOMMODATE

and Under Eyelids with my fingers at a difiance from each
other, and then repeated my effort to read the Book ; but
found I could not do it. That is, my Eyes were fo near to
the Book, that, although I attempted to exert all the means
before enumerated, the Eyes were not fo much altered in
their conformation a-s to render the vifion difiindt. In this
Experiment, no part of the Cornea was covered by the Eye-
lids, for the Eyelids were at the difiance of Half an Inch
from each other.

EXPERIMENT II.

In this Experiment, I kept my head in the fame pofture,
and at the fame di fiance from the Book, as in the former
Experiment ; but I acted with the Orbicularis Palpebrarum,
fo as to bring the Edges of the Eyelids within a Quarter of
an Inch of each other, and then made an exertion to read,
and found I could fee the Letters and Words diftindly.

E X-

THE EYE TO THE DISTANCES OF OBJECTS.

135

EXPERIMENT III.

In this Experiment, I kept my head in the fame pofiure,
and at the fame diftance from the Book, as in the two for-
mer Experiments ; but, inftead of employing the Mufcular
Contraction of the Orbicularis Palpebrarum, I brought the
Edges of the Upper and Under Eyelids within a Quarter of
an Inch of each other, by means of my fingers, and then
ftretched the Edges of the Eyelids fo as to make Prefiure
on the Upper and Under Edges of the Cornea ; and found,
that the Letters then appeared difiinCt.

As, in all thefe Experiments, the Difiance of the Eye
irom the Object, and the Quantity of Light, were the fame ;
as no Part of the Pupil was covered by the Eyelids, fo as
to cut off the mod diverging Rays ; as the ObjeCt appear-
ed confufed when the Orbicularis was not contracted ; and
difiinCt on its contracting j — there can be no doubt that

R 2. the.

MEANS BY WHICH WE ACCOMMODATE

136
*

the Adtion of the Orbicularis helps to accommodate the Eye
for feeing near Obje&s more diflindtly *.

SECT.

* On the ift day of May 1794, Dr David Hosack read to the Royal Society
of London, Obfervations on Vifion, in which (Phil. Tranf. 1794, Part II. xv,
p. 222.) he writes as follows : “ With a Speculum, I made preflure on the Eye,

“ while dire&ing attention to an Object twenty yards diftant, and faw it diftindtly :
“ but, endeavouring to look beyond it, every thing appeared confufed.

“ I then increafed the Preffure confiderably, in confequence of which I was
“ enabled to fee objects di&indtly at a much nearer than the natural focal diftance ;
“ for example, I held a Book before my Eye at the diftance of two inches. In
“ the natural ftate of the Eye, I could neither diftinguifh Lines nor Letters : but,
“ on making Preflure with the Speculum, I was enabled to diftinguilh both Lines
“ and Letters of the Book with eafe.”

I find myfelf, therefore, under the difagreeable neceflity of adding, That I men-
tioned the above Experiments, in my Public Courfe of Lectures, on the 27th day
of April 1789: — That I have repeated the mention of them in every Courfe of
my Lectures fince that time : — That Dr Wheaton Bradish, in his Inaugural
Differtation “ De Vifu,” publifhed on September 12. 1792, and which I did not
read till it was publifhed, mentions, in p. 39. thefe opinions, which I had propofed
in my Leftures, in the following words: “ Lortge veto ante alias enitefcit fenten-
a tia, qure interni auxilio cujufvis fpreto, Mufculos quofdam Oculi externos, obliquos
u nempe, infuper et Orbicularem, hos limul prteftare effe&us afleruit. Tali mcdo

“ Oculi

THE EYE TO THE DISTANCES OF OBJECTS. 137

SECT. VIIL

Upon the whole : it appears to me,

1. That the Iris, by leflening the Pupil, and intercepting
the moll diverging Rays of Light, renders the Pidure of
near Objeds more diftind.

2. That the Redi Mufcles, by their adion, lengthen the
Axis, becaufe they prefs chiefly on the Sides of the Eyeball j
and, further, the Cornea is not only more dilatable than the
Sclerotic in general is, but it will be found that the Scle-
rotic, in Man and other Animals, is thinner and more di-
latable, in its Anterior Part, and in its Pofterior Part where
the Pidure is formed, than it is on its Sides.

3. That

“ Oculi Axin augeri, Corneamque convexam magis quam antea reddi.” — That Dr
David Hosack attended my Courfe of Lectures the winter after Dr Bradish
publithed his Inaugural Differtation, to wit, 1792-3, which was finifhed upwards
of a year before Dr Hosack read his Paper to the Royal Society.

I3s MEANS BY WHICH WE ACCOMMODATE, &c.

3. That the two Oblique Mufcles forming an Oblique
Girth around the Eyeball, between the Lens and Bottom of
the Eye, muft, by their Preflure, increafe the Didance of
the Lens from the Retina, or increafe the Length of the
Pofterior Part of the Axis of the Eyeball.

4. The Orbicularis Palpebrarum renders the Fore and Mid-
dle Part of the Cornea, oppolite to the Pupil, more Convex ^
and increafes the Length of the Anterior Part of the Axis
of the Eyeball. And it is evident that all thefe Means may
concur in forming perfed Villon.

CHAP.

CHAP. IX.

Of the Lachrymal Du£ts.

SECT. i.

"^C^ERY eminent Authors, Haller and Zinn, having Part-
ed their doubts of the Exiftence of Duds from the
Glandula Innominata of Galen I was led to examine the

fubjed

* Haller, in Pr. Lin. Phyf. Cap. xviii. § 498. “ Lachrymam partial ar-

S( teriae conjunctivas tunicae exhalant, partim creditur deponere Glandula,” &c.
In Homine nondum fatis certo, neque mihi unquam vili funt DuCtus.”

T. G. Zinn,

140

OF THE LACHRYMAL DUCTS.

fubjeci with accuracy ; and, after finding one large Duct
from it in Birds, I difcovered a number of fmall Duds from
it in the Human Body, running nearly parallel with each
other, and terminating on the Inner-fide of the Upper Eye-
lid, not far from the External Canthus of the Eye*.

After introducing Briftles into fome of them, 1 injeded
Quickfilver into a few others ; and I ftill preferve the Pre-
parations I made then, and have demonftrated them, fince
that time, annually in my Public Courfes of Ledures. In
17 58, I publilhed a Defcription of them *, illuftrated by the
Figures reprinted in Table IV. of this Paper.

SECT.

T. G. Zinn, de Oculo, Cap. xiii. §1. “ Lachrymas maxima certe ex parte

“ exhalare videtur arteriae conjun&ivas,” &c* “ In Homice autem hue ufque

“ accuratiffimorum Anatomicorum aciem Du&us illi effugerunt : neque mihi, hac
“ in re, illis feliciorem efle contigit.”

~ * Obfervations Anatomical and Phyfiological, 1758, 8vo.

OF THE LACHRYMAL DUCTS.

141

SEC T. II.

* '

Since that time, finding that the error had been commit-
ted, by the greater number of Anatomifts and Surgeons, of
fuppofing, that the Two Duds which lead from the Punda
are united before they enter the Lachrymal Sac ; and think-
ing, that, in certain cafes, it might be material in the cure,
that the Surgeon knew that one of thefe Duds might be
pervious, though the other was obftruded ; I had an ac-
curate Drawing of them, and of the Lachrymal Sac, and
Nafal Dud, made, which the Reader will find in Table V.
Fig. 1. And, in Fig. 2. and 3. of the fame Table, the ap-
pearance of the Termination of the Nafal Dud is delL
neated.

SECT. III.

To trace fully the courfe of the Tears, Two other Canals,
I apprehend, remain to be defcribed ; I mean the Dudus
Incifivi. In Quadrupeds, as in the Ox and Sheep, thefe are

Two

142

OF THE LACHRYMAL DUCTS.

Two Large Canals, open at both ends, and palling obliquely
downwards from the Nofe into the Mouth, reprefented in
Tables VI. and VII.

In by far the greater number of Human Subjects, of dif-
ferent ages, I have not been able to find any vefiige of fuch
Duds, in the Bottom of the Nofe, or Roof of the Mouth :
But, in a few fubjeds, I have found them, open at both ends,
but always very much fmaller than in the Quadruped. In
fome of thefe, I palled a Briftle or Small Probe, very readi-
ly, from the Nofe into the Mouth. In two or three fub-
jeds, I firft poured Quickfilver from the Nofe, through the
Dudus Incifivus, into the Mouth; and then, with a fmall
Syringe, injeded through it Melted Wax, coloured with Ver-
milion : And thefe Preparations, which I have preferved

and demonftrated for a great number of years, are accurate-
ly delineated in Table V. Fig. 4, 5, 6, 7.

SECT. IV.

In Man, and in the Quadruped, the Lachrymal Duds are
always direded towards the Forepart of the Nofe, and ter-

minate

OF THE LACHRYMAL DUCTS,

minate over the Dudus Incilivi j and the Dudus Incilivi
begin from Cups or Funnels* which form the Lowermoll
Parts of the Bottom of the Noftrils : So that, beyond all

doubt, the Tears are applied to and pafs through them into
the mouth 3 and it feems by no means improbable, that the
Dudus Incilivi, like the Punda Lachrymalia and Duds
through which the Tears are conveyed into the Nofe, may
be excited into adion by that kind of Irritation which the
Tears give. Why they are always found, and large, in the
Quadruped 3 yet generally wanting, and always fmall, in
Man 3 cannot, without farther obfervation, be fatisfadorily
explained.

u»

EXPLANATION

OF THE

TABLES,

■ « .

Explanation of Table L

* | ''HE Firft Four Figures of this Table reprefent the Eye
of an Ox diffeded. The Fifth, Sixth, and Seventh
Figures reprefent the Human Eye0

FI Go

146

EXPLANATION OF TABLE I.

FIG. 1.

Reprefents the Left Eye of an Ox, viewed obliquely from
above.

a The Trunk of the Optic Nerve.

b c The Outer Part of the Sclerotic Coat.

d e The Cut Edge of the Sclerotic Coat.

f § A Se&ion of the Root of the Cornea.

h The Cryftalline Lens, feen at the Pupil, inclofed in

its Capfule.

i The Inner Radiated Part of the Iris.

k The Sphinder Mufcle of the Iris.

I m The Outer-Iide of the Choroid Coat.

a The

EXPLANATION OF TABLE I.

147

n The Ciliary Circle, joining the Choroid Coat to the

Root of the Iris, and Both thefe Coats to the
Sclerotic Coat.

0 A Portion of the Iris inverted, after cutting it.

p The Ciliary ProcefTes of the Choroid Coat, the Ex-

tremities of which float in the Pofterior Chamber
of the Aqueous Humour, or between the Back-part
of the Iris and the Cryftalline Lens.

q The Retina iffuing from the Optic Nerve.

r The Middle Part of the Retina.

/ The Choroid Coat, lined with its Black Paint, be-

tween the Ciliary Circle and the Continuation of
the Retina forwards.

EXPLANATION OF TABLE I.

T Ao
14^

In FIG. 2.

The fame Eye is reprefented more fully difletfled.
a Reprefents the Trunk of the Optic Nerve..

b c The Sclerotic Coat cut and turned aflde.
d e A Sedion of the Cornea near its Root.

f The Under Half of the Iris.

g The Cryftalline Lens inclofed in its Capfule.

h i The Outer-hde of the Choroid Coat.
k l The Ciliary Circle.

m The Ciliary Procelfes, with their Extremities floating

in the Aqueous Humour between the Iris and the
Lens.

n A

EXPLANATION OF TABLE I.

149

n, A Portion of the Iris inverted.

# The Extremities of a Number of the Ciliary Pro-

ceffes inverted, to fliew how far they are loofe.

p The Middle Part of the Retina.

q The Doublings or Ciliary Procefles of the Retina,

from which the Black Paint, lining the Ciliary
Proceffes of the Choroid Coat, is walked off.

r The Ciliary Proceffes of the Retina divided into

Minute Fibres, which are inferred into the Anterior
Part of the Capfule of the Gryftalline Lens.

EXPLANATION OF TABLE L

' 150

In FIG. 3.

After removing the Cornea, the Iris, the- Choroid Coat with
its Paint, and inflating the Canal difcovered by Dr Petit,
a Fore View is given of the Cryflalline Lens, with the Ter-
mination of the Retina, by Doublings or Ciliary Procefles,
in the Forepart of the Capfule of the Lens, a very little
within its Outer Edge.

a Reprefents the Forepart of the Cryflalline inclofed in

its Capfule.

b c The Vitreous Humour covered by the Retina.

d A Hole cut in the Forepart of the Canal of Petit,
by which it was inflated.

e f The Circular Canal of Petit inflated, to fhew that it is
not Cylindrical, but Cellular, fomewhat refembling
the Colon.

g h The

EXPLANATION OF TABLE I.

151

g h The Doublings or Ciliary Proceiles of the Retina,
adhering to the Anterior Layer of the Capfule ot
the Vitreous Humour, and, with that, forming the
Forepart of the Canal of Petit.

i The Minute Terminations of the Ciliary Proceiles of

the Retina, in the Anterior Part of the Capfule of
the Lens, very near to the Outer Edge of the
Lens.

FIG. 4.

In this Figure, a Side View is given of the Cryftalline
Lens and Vitreous Humour adhering together, and their
Capfules entire.

a b The Vitreous Humour inclofed in its Capfule.
g The Forepart of the Cryftalline Lenp.

T 2

d e The

EXPLANATION OF TABLE I.

The Roots of the Ciliary Procefies of the Retina,
with fome of the Black Paint of the Choroid Coat
adhering to their Outer Side, and the Anterior
Layer of the Capfule of the Vitreous Humour
lining them.

The Infertion of the Retina, with the Anterior Lay-
er of the Vitreous Humour, in the Forepart of the

Capfule of the Lens.

✓

An Oblong Hole cut in the Outer Part of the Canal -
of Petit, through which the Outer Edge of the
Lens is feen, covered with its proper Capfule,
forming the Inner-fide of the Canal of Petit.

The Anterior, and k the Pofierior, Layer of the
Capfule of the Vitreous Humour, fixed to the Cap-
fule of the Lens at a confiderable diftance from
each other. Hence it appears, that the Forepart
of the Canal of Petit is formed by the Anterior
Layer of the Vitreous Humour, covered by the
Retina ; the Pofierior Part of it, by the Vitreous
Humour, covered by the Pofierior Layer of its

Capfule 3

EXPLANATION OF TABLE I.

553

Capfule and that the Xnner-hde of it, is formed
by the Edge of the Cryilalline, covered by its
proper Capfule only,, where its greatefl Diameter
is found, or where the Two Lenfes which com-
pofe it are conjoined.

I The Backpart of the Cryilalline Lens feen through

the Vitreous Humour.

FIG. 5. & (L

In thefe Figures, the Connexion of the Coats of the Hu-
man Eye is reprefented. In Fig. 5. the Parts are repre-
fented of their Natural Size : In Fig. 6. they are magni,

fed to Two Diameters.

a The Optic Nerye,

b c The Sclerotic Coat, cut and turned afide>

d The Cut Edge of the Cornea.

e- The :

EXPLANATION OF TABLE I.

The Iris.

The Forepart of the Lens.

The Outer Sides of the Choroid Coat.

The Ciliary Circle.

The Iris cut and turned backwards.

The Ciliary Procefles of the Choroid Coat in their
natural fltuation, with their Extremities floating
loofe in the Aqueous Humour, and covering the
Outer Edge of the Lens.

The Extremities of the Ciliary Procefles turned back,
to fhew how much of them is loofe, or unconnedt-
ed with the Parts on the Inner-fide of them.

The Middle Part of the Retina.

The Anterior Part of the Retina, conne&ed to the
Capfule of the Lens by the Fibrous Extremities of
its Ciliary Procefles.

FIG.

EXPLANATION OF TABLE I.

i55

ajnr" £/sm j&t tvmvz?irxia&

FIG . 7.

This Figure reprefents the Retina lining the Pofcerior

Part of the Ciliary Procelfes, and inferred into the Capfule

of the Lens.

a b The Inner-fide of a Part of the Sclerotic Coat*

c d The Ciliary Proceffes of the Retina, on the Inner-
fide of the Paint which lines the Ciliary Proceifes
of the Choroid Coat.

/ The Pofterior Part of the Cryftalline Lens inclofed

in its Capfule.

e The Fibrous Extremities of the Ciliary Precedes of

the Retina, in their courfe, over the Edge of the
Cryftalline Lens, to their Terminations in the
Forepart of its Capfule.

Explanation

156 EXPLANATION OF TABLE I.*

Explanation of Table I.

FIG. I.

» Reprefents the Human Eye difleded.
a The Optic Nerve.

h b The Sclerotic Coat, cut and turned outwards.

c The Sclerotic Coat, cut and turned forwards with

the Cornea d.

js e One-half of the Iris in its place.

/ The

TAB. I. *.

(L c&A

' ■ %

I g

H H

7)1

EXPLANATION OF TABLE I.* 157

The Pupil and Cryltalline Lens in its place.

The Ciliary Circle.

The Choroid Coat.

The Ciliary Procelles feen in their places, by cutting
off a portion of the Iris.

A Portion of the Iris cut and turned back.

The Floating Points of the Ciliary Procelles turned
backwards.

The Middle Smooth Part of the Retina, feen by
cutting a Hole in the Choroid Coat,

The Roots of the Ciliary Procelles of the Retina, to
which the Black Paint of the Ciliary Procelles of
the Choroid Coat adheres.

The Ciliary Procelles of the Retina, inferted into the
Capfule of the Cryftalline Lens.

FIG.

153

EXPLANATION OF TABLE I.*

■e

FIG. 2.

Reprefents, chiefly, the Circle of Petit in the Human Eye.

a a The Vitreous Humour inclofed in its Capfule.

b The Cryftalline Lens inclofed in its Capfule.

c The Ciliary Procefles of the Retina inferted into the

Capfule of the Cryftalline Lens.

d The Circular Canal of Petit inflated.

e A Hole cut in the Circular Canal of Petit, at which

the Air Amending' it was blown in.

Explanation

€>

tab.il

EXPLANATION OF TABLE XL

159

Explanation of Table II.

Fig. i. reprefents the Forepart, and Fig. 2. the Backpart,
of the Iris of an Ox, of its Natural Size.

In FIG. 1.

A A Reprefents the Cut Edge of the Sclerotic Coat.

B B The Pupil,

C C The Sphinder Mufcle of the Iris.

D D The Inner Part of the Iris, in which the Fibres are

radiated, without any appearance of a Sphinder
Mufcle.

U 2

i6o

EXPLANATION OF TABLE II.

In FIG. 2.

A A Reprefents the Inner-fide of the Anterior Part of the
Choroid Coat.

B B The Ciliary Proceiles.

C C The Pupil.

D D The Outer and Back Part of the Iris, which conlifts
of Vafcular and Radiated Fibres that conceal the
Sphin&er Mufcle.

E E The Inner and Back Part of the Iris, compofed, like
its Forepart, of Radiated and Vafcular Fibres.

Explanation

dclr*

rcAtleJ^ tfc ■

EXPLANATION OF TABLE III.

161

Explanation of Table III.

The Two Figures in this Table reprefent the Pofierior
Part of the Human Iris, delineated by Mr Fyfe. Fig. i.
Ihews it of the Natural Size, and Fig. 2. reprefents it Mag-
nified.

A A The Inner-fide of the Anterior Part of the. Choroid
Coat.

B B The Ciliary Procefies.

C C The Veflels and Radiated Fibres.

D D The Mufcular Sphincter of the Irisa,

E The Pupil,

Explanation

1 62

EXPLANATION OF TABLE IV.

Explanation of Table IV.

This Table reprefents the Right Eye with its Mufcles,
viewed obliquely from its Upper and Outer Side.

a Reprefents the Eyeball.

b Part of the Upper Eyelid.

c The Optic Nerve.

d The Attollens Falpebram Superiorem drawn alide by

a Pin.

e The Redus Attollens Oculum.

/ The Redus Abdudor Oculi.

S The

tab.iv:

✓

EXPLANATION OF TABLE IV. 163

The Redus Addudor Oculi.

The Rectus Beprimens Oculurn.

The Flelhy Belly of the Obliquus Superior Trochlea**
ris.

The Trochlea, fixed to the Os Fronds, with the Ten-
don palling through it.

The Infertion of the Tendon of the Trochlearis in
the Eyeball.

The Inferior Oblique Mufcle taking its 'rife from the-
Superior Maxillary Bone.

The Infertion of the Tendon of the Inferior Oblique
Mufcle in the Eyeball,

Explanation

164

EXPLANATION OF TABLE V.

Explanation of Table V.

FIG. 1.

Reprefents the Upper Eyelid of the Right Side of the Human
Subjedl, with the Glandula Innominata Galeni, or Lachry-
mal Gland.

a The Inner-hde of the Upper Eyelid.

p The Two Pundta Lachrymalia, into which the dif-

ferent Ends of a Bit of Wire are introduced.

b Part of the Under Eyelid.

c The External Canthus.

d The Thicker Conglomerated Part of the Lachrymal
Gland.

e A

S%-JA£c//c%J /

■ 4

■j

EXPLANATION OF TABLE V.

165

A Number of Smaller Lachrymal Glands, lying be-
tween d and the Conj undiva, which, for diftinc-
tion’s fake, I fliall call Glandulae Lachrymales Con-
gregatae.

Four Briftles introduced into the Duds of the La-
chrymal Gland.

One of thefe Duds, into which Quickfilver was in-
jeded, which is hid where it paffes between the
Glandule Congregatae e% but appears again, where
it comes out of the Glandula Innominata, com-
pofed of Three Branches.

A Part of the Tunica Conjundiva, at which, before
the Preparation was immerfed in Spirits, the Ori-
fices of two or three very fmall Lachrymal Duds,,
could be perceived.

F I G,

a66

EXPLANATION OF TABLE V.

FIG. 2.

Reprefents the like Parts on the Left Side, viewed from the
Upper and Outer Side.

a The Outer Side of the Tunica Conjunctiva of the

Left Eye.

be ddee The fame as in Fig. I.

/ The Artery of the Lachrymal Gland injeded.

g The End of a Brittle put into one of the Lachrymal

Duds b, after I had injeded the Dud with Quick-
filver.

i i Two Branches joining to compofe the Dud h.

F I G.

EXPLANATION OF TABLE V.

167

F I G. 3.

Reprefents the Right Eye of the Common Hen,

a An Outline of the Comb and Beak,

b The Eyebalh

c The Eyelids,

d The Membrana Niditans.

e A Probe palled into the Dud of the Lachrymal

Gland,

/ A Probe pafled into the Undermoll Pundum La-

chrymale,

g A Probe palfed from the Uppermoft Pundum La-

chrymale into the Nofe^ and from the Nofe into,

the Mouth.

EXPLANATION OF TABLE V.

In FIG. 4.

Represents the Bottom of the Eyeball in the fame
Fowl.

The Optic Nerve.

The Lachrymal Gland.

Part of the Membrana Nidlitans.

A Probe paiTed into the Lachrymal Du6h

Explanation

f 'N

. ;

EXPLANATION OF TABLE VL

169

Explanation of Table VL

In FIG, 1,

A Reprefents the Upper and B the Under Eyelid.

C D Bridies introduced into the Two Punda Lachryma-
lia, and the Duds from them cut open.

E F The Termination of thefe Duds in the Lachrymal
Sac, by two diftind Orifices.

G FI I The Lachrymal Sac and Nafal Dud laid open*

£7°

EXPLANATION OF TABLE VL

In FIG. 2. Sc 3.

The Termination of the Nafal Lachrymal Du <51 in the Nofe
is feen at E E, under the Os Spongiofum Inferius D,

FIG. 4.

ABBC Reprefents Part of the Septum Narium.

D The Mouth of the Left Euftachian Tube.

E The Superior, and F the Inferior, Os Spongiofum of

the Left Side.

H I K The Du&us Incifivus of the Right Side laid open,
after palling a Brillle through it.

F I G,

EXPLANATION OF TABLE VI

172

F I G. 5.

A B Reprefents the Septum Narium cut horizontally.

C D The Upper Orifices of the Du&us Incifivi.

E The Dentes Incifivi.

FIG. 6.

By cutting off the Foreparts of the Upper Jaw-Bones, the
Du&us Incifivi are feen, with Probes paffed through them
from the Bottom of the Nofe into the Mouth,

A The Bottom of the Septum Narium cut horizontally,

B C The Bottom of the Cavity of the Nofe.

de&fg Briftles paffed through the Ductus Incifivi.

F I G.

EXPLANATION OF TABLE VI.

172

FIG. 7.

In this Figure, the Openings of the Dudtus Incifivi into
the Mouth are reprefented, from a Perfon, very far advanced
in life, who had loft all the Teeth of both Jaws.

a b The Lower Orifices of the Du&us Incifivi.

Explanation

\ ’

* I

EXPLANATION OF TABLE VII.

Explanation of Table VIL

FIG. i.

A Reprefents the Upper-Lip of the Ox,

173

The Callous Gum.

C The Roof of the Mouth,

E E The Natural Openings of the Two Dudus Incilivi,

F The Under Part of the Right Dudus Incilivus cut:
open its whole length.

Xii

I74

EXPLANATION OF TABLE VIL

In F I G. 2.

A Reprefents the Upper Lip of the Sheep.

B The Callous Gum.

C The Roof of the Mouth.

E The Natural Termination of the Left Dudtus Incifi-
vus.

F A Probe palled from the Nofe, through the Right
Du&us Incifiyus, into the Mouth,

Explanation

TAB. -Mil

EXPLANATION OF TABLE VIII.

Explanation of Table VIII.

In this Table, the Right Lachrymal Nafal Du6l of a
Sheep is traced to its Termination in the Nofe ; which,
when the Face of the Animal is placed horizontally, will be
found to be over the Bottom of the Nofe, a very little be-
hind the Upper End of the Dudtus Incilivus,

a Reprefents the Os Nafi of the Right Side cut.

b The Os Spongiofum Inferius.

c The Eyelids.

d e Probes palled through the Pundta Lachrymalia into
the Lachrymal Sac, ,

/ g The

176

EXPLANATION OF TABLE VIII.

f g The Lachrymal Nafal Dud laid open.

h i A Probe pafled from the Lachrymal Dud into the

Cavity of the Nofe.

hi A Probe palled through the Canalis Inciiivus.
m The Fiflure in the Upper Lip.

THE END OF TREATISE SECOND.

OBSERVATIONS

ON THE

ORGAN

O F

HEARING

I N

i -

M A

AND

OTHER

ANIMALS,

BY '

. |

ALEXANDER MONRO, M. D.

PROFESSOR OF MEDICINE, ANATOMY, AND SURGERY,
IN THE UNIVERSITY OF EDINBURGH,

EDINBURGH:

PRINTED BY ADAM NEILL AND COMPANY

3 797

•<

■

A Table of the Contents of Treatife 111

Page

PREFACE, - - - - - 181

C H A P. I.

Of the Size, Shape, and Relative Situation, of the Ca-
vities of the Ear, - ~ - - 187

CHAP. II.

Of the Structure of the Human Cochlea, = 189

CHAP. III.

Of the Ear in Whales, - 203

CHAP. IV.

Of the Ear in Cartilaginous P'ilhes, - 207

CHAP. V.

A Summary of the Chief Circumflances above defcribed, 213

CHAP.

CONTENTS OF TREATISE III.

180

CHAP. VI.

Atteftation as to the Fadts above defcribed,

Page

219

CHAP. VII.

Remarks on Profeflor Scarpa’s Book on the Ear, 225

Explanation of the Tables,

241

PREFACE.

QO far back as the year 1756, whilft I was in Berlin, ob-
ferving, that no Anatomift had traced the Difiribution
of the Portio Mollis of the Auditory Nerve within the Co-
chlea, Veftible, and Semicircular Canals; or, that the Struc-
ture of thofe principal parts of the Ear on which ultimately
Imprefiion is made, and to which all the other pieces of its
complex and elegant machinery are fubfervient, was unknown;
I began to inveftigate the fubjedt with accuracy, and foon
found the means of tracing the progrefs of the Portio Mol-
lis, the minute branches of which I profecuted upon the
Cochlea chiefly,

A a

From

PREFACE.

182

From that time downwards, I have demonftrated thefe an-
nually, in my Courfes of Le&ures in this Univerfity ; and,
in 1783, when I publifhed my Obfervations on the Nervous
Syftem, I gave a Defcription of thefe Preparations, illuftra-
ted by Figures, (See Tables XXIX. XXX. & XXXI.) j
and, before publication, I fhewed my Preparations to feveral
excellent judges.

Two years thereafter, in 1785, in a Work I publiihed on
the Structure and Phyliology of Fifhes, compared with thofe
of Man and other Animals ; I defcribed the Parts of the
Ear in the Whale, in Amphibious Animals, and in Fifhes 3
and illuftrated my Defcriptions with a Number of Figures.
(See Tables VII. XXXIV. XXXV. XXXVI. XXXVII.
XXXVIII. & XXXIX.)

Soon thereafter, to-wit in 1787, I received a Letter from
the late Dr Camper, in which he denies the exigence of
Semicircular Canals in Whales, and calls in queftion that of
the Meatus Auditorius Externus in the Skate and Squalus
Squatina, which I had defcribed.

I fhould

PREFACE,

1S3

I fliould not have pointed out to the Public what I knew
to be erroneous in Dr Camper’s Letter, if he had not, at
the fame time, written me, that he intended to have his Re-
marks inferted into a German Tranflation of my Book on
Fifties, which he told me was then about to be publiftied by
Dr Schneider, “ in order to put me right, and to be ufe-
“ ful to others

Still later, in 1787, Dr Antonius Scarpa, Profeftor of
Anatomy and Surgery in Pavia, Ticinum, in a large Work,
entitled, “ Difquifitiones Anatomicse de Auditu et Olfadlu,”
illuflrated with many Tables, has reprefented the Defcription
I had given of the Human Ear as inaccurate ; and the whole
of my Account of the Meatus Auditorius Externus, and of
the Communication of it with the Interior Parts of the Ear,
and of thefe with each other, in the Cartilaginous Fifties, as
a mere fi&ion.

A a 2 Although •

* I obferve this Tranflation, by J, G„ Schneider, with Dr Camper’s Notes,
quoted by Dr Soemmering as publiflied, in 1787, at Leipfic ; but I have not
yet feen it.

184

PREFACE.

Although, from the attention I had paid to thele fubjeds,
and that I had in my pofleflion the feveral Preparations from
which my Defcriptions were taken, and had demonftrated
thefe publicly in my Courfes of Ledures, and privately to
many good judges of fuch matters ; yet, the reputation
which Dr Camper and Dr Scarpa have acquired, made it
neceflary for me, on my own account, and likewife to pre-
vent others from being milled, by their authority, on thefe
highly curious and interelling parts of Anatomy, to refume
my refearches on thefe fubjeds.

The Public will reap the advantage of having thefe organs
more fully defcribed, and of feeing them more elegantly deli-
neated, than in my former Figures, by my allillant Mr Fyfe,
from recent Preparations, which, at my requeft, he under-
took to make ; and which he has, by my direction, exe-
cuted with great dexterity and accuracy.

All the Preparations from which the Figures I formerly
publilhed, or which I now publilh, have been taken, are Hill
in my pofteftion. They have all been lately demonftrated to
the Members of the Royal Society of this place, and mi-
nutely examined by fuch Members as are beft qualified to
judge of fuch fubjeds, after they were made acquainted with

the

PREFACE.

the doubts raifed by Camper and Scarpa, and that their
atteftation as to fads would be requeued.

I fhall now proceed to defcribe the Structure of fome of
the principal Parts of the Ear, in Man and in other Ani-
mals j I fhall then add the atteftation, as to the accuracy
of my Defcription and Tables, of thofe Members of the
Royal Society, who have examined my Preparations, and Fi-
gures taken from them ; and I fhall conclude with a few.
Obfervations on Profeffor Scarpa’s Work.

TREATISE

TREATISE THIRDs

ON THE EAR.

CHAP. L

Of the Size, Shape, and relative Situation*
of the Cavities of the Ear.

rTT',HAT the Size, Shape, and relative Situation, of the Ca-
vities of the Ear, might be more diftinddy perceived
than they can be by cutting the Bones in the common way,
I propofed to my Son, to fill them with Metal, and then to
deftroy the Bone ; which he executed very dexteroufiy and
fuccefsfully : And in Four Figures of Table h an exact

Reprefentation

1 83 SIZE, &c. OF THE CAVITIES OF THE EAR.

Reprefentation is given of his Preparation, from Drawings
of it by Mr Fyfe ; to which, with its Explanation, I fhall
refer the Reader. The Cochlea, in particular, is fo com-
pletely filled as to give an excellent view of its Size and
Figure.

In Table II. I have reprefented the appearance of Caverns
in different kinds oT Quadrupeds, refembling in office thofe
of our Mafloid Procefs. Thefe are, in proportion, confider-
ably larger, and their fides thinner and more elaftic, than in
Man j and there can be no doubt, that the greater Acute-
nefs of thofe Animals in Hearing, is, in part, owing to the
Strudure of thefe Caverns.

CHAP.

CHAP. II.

Of the Structure of the Human Cochlea.

SECT. i.

TT has been long known, that the Human Cochlea defcribes
-** two complete Gyri or Turns, and a Half Turn ; that a
central conical ofleous Pillar, called Modiolus , is continued
to the Middle of its Second Gyrus ; that the Gyri are di-
vided, by a Partition called Lamina Spiralis, into Two Wind-
ing Canals, called Scales ; that one Scala begins from the
Veftible, and is therefore called Scala of the Vejlible , and that

B b the

I90 OF THE STRUCTURE OF THE HUMAN COCHLEA,

the other begins at the Foramen Rotundum in the Backpart of
the Cavity of the Tympanum , and is therefore called the Sc ala
of the Tympanum; that the Scalce are Wider at the Veflible
and Foramen Rotundum than at the Apex of the Cochlea,
or, that they are of a Conical figure that at the Apex of
the Cochlea they communicate with each other, by opening
into a Common Tube, called Infundibulum or Funnel, one End
of which begins at the Termination of the Modiolus, and the
other End of it is fixed to the offeous Top or Cupola of the
Cochlea,

SECT. II.

It is evident, that the Offeous Structure of the Human
Cochlea muft be fully explained, before we can defcribe its
Membranes and Courfe of its Nerves ; and as fome material
circumftances have efcaped the obfervation of Authors, I
ihall give a fnort Defcription of this, illuflrated by Fi-
gures.

The Central Pillar of the Cochlea confiffs of Two Parts,
called Modiolus and Infundibulum.

The

OF THE STRUCTURE OF THE HUMAN COCHLEA. i9i

The Modiolus is not a folid OHeous Cone, as has been ge-
nerally fuppofed, but may be conlidered as a Hollow Cone,
containing that Branch of the Portio Mollis which is de-
fined for the Cochlea ; and is everywhere Cribriform, for
the Paflage of the Branches of that Nerve. The Infundibu-
lum is an imperfect Oileous Funnel, connected to the Top of
the Modiolus. So that the Modiolus and Infundibulum are
Two Hollow Conical Bodies, connected together by their

fmall Ends. The Plate which is between them, and in the

Centre of both, is Cribriform. Around the Modiolus, the
Firft Gyrus of the Cochlea and Half of the Second Gyrus
are defcribed ; the other Half Gyrus inclofes the Root of
the Infundibulum; and the Upper Ends of the Gyri, which
communicate with each other, are covered or inclofed by
the Cupola of the Cochlea,

The Partitions of Bone which feparate the Gyri from each
other, are not compofed of One Solid Plate, as Authors have
reprefented *, but conlift of Two Plates, conneded to the
Modiolus at fome diflance from each other,

B b 2 The

* Du Vernet. — Cassebohm, T. 5. F. 7, 8, 9, 10.— Scarpa, P. 10. F. 3. 7.

192 OF THE STRUCTURE OF THE HUMAN COCHLEA.

The Olfeous Root of the Lamina Spiralis is likewife com-
pofed -of Two Plates, connected to the Modiolus or Root of
the Infundibulum, at fome diltance from each other.

I have already obferved, that the Modiolus is compofed of
a Cribriform Hollow Cone, the Sides of which confift of Two
Thin Plates ; and the Holes in it are much more Nume-
rous than they have been defcribed to be by Authors, and
are not difpofed in the Regular Manner they have repre-
fented them

They are to be feen in every part of the Surface of the
Modiolus ; but are mod numerous clofe to the Roots of the
Olfeous Septa which feparate the Gyri from each other ;
and clofe to the Outer Sides of the Root of the Lamina
Spiralis. They are numerous in the Plate between the Mo-
diolus and Infundibulum ; and when the Olfeous Septa and
Lamina Spiralis are cut near the Modiolus, they are feen in
the Side of the Modiolus, between the Two Plates which
compofe the Septa and Lamina Spiralis.

* Cassebohm, T. 5. F. 1C.

OF THE STRUCTURE OF THE HUMAN COCHLEA. 393

in Table III. the Ofleous Strudure of the Cochlea is accu-
rately reprefented, magnified to Five Diameters ; and a full
Explanation of it is annexed, to which I fliall refer the
Reader.

SECT. III.

It had been, and ftill is, generally fuppofed, that the For-
tio Mollis is distributed upon the Periofteurn lining the Co-
chlea and Semicircular Canals : But, the extraordinary

Hardnefs and Thicknefs of thele Bones, the Smallnefs of the
Holes by which the Nerves enter, and the great Delicacy
and Tendernefs of the Membranes within the Cochlea, — had
prevented Anatomists from tracing the Courfe of the Bran-
ches of the Portio Mollis within the Os Petrofum, and from
perceiving the nature of the Interior Membranes, and the.
manner in which the Nerves terminate upon thefe.

194 OF THE STRUCTURE OF THE HUMAN COCHLEA.

To fhew the Reader how little was known upon thele
fubje&s, I fhall quote, at the bottom of the page, the ac-
count given of them by the mo ft eminent Anatomifts of the
prefent century * **.

* Valsalva, de Aure Humana, Cap. iii. § 14. “ Vidique demum minima

u quaedam foramina, per quae nerves; fibrillae Coehleam fubeunt. Intra

“ hanc vero eaedem probabiliter in membranam expanfae.”

Winslow, Exp. An. P. 2. S. x. § 409. 1732. “ La Portion Molle du Nerf

“ Auditif aboutit par fon tronc a la grande foiTette du Trou Auditif Interne, ou
“ les filets de ce tronc pafifent par plufieurs petits troncs de la bafe du Lima^on,
“ en partie au Periofte des Canaux demicirculaires, en partie au Periofte Interne
“ des demi-canaux du Limagon.” He fays nothing of their appearance or diftri-
bution on this Periojieum.

Casjeeomm, de Aure Humana. 1734- Tr. v. § 227. “ Neque in Cochlea

<£ Humana filamentum nerveum unquam obfervavi.”

Haller, El. Phyf. Lib. xv. § 38. 1763. “ Nervum autem aliquem in con-

fpicua filamenti fpecie, per Cochlea fpiras circumduci, (uti pingit Valsalva),
“ nunquam vidi. Sed nequidem, mantis Anatomicae, etiam fumma induftria, Ner-
« vulos ex modiolo per foramina, jam a nobis expofita, aut in fcalam cochleae alter-
£< utram, aut in duplicis laminaeque fpiralis membranaceum complementum, effi-

** cientis perioftei intervallum duxerit.”

Haller,

OF THE STRUCTURE OF THE HUMAN COCHLEA* 195

SECT. IV.

As, previous to 1756, when I firft attempted to trace the
Portio Mollis within the Cochlea, I had repeatedly rendered

Injected

Haller, in Pr. Lin. Phyf. § 493. “ Alter ramus, qui Cochleae fulcum fubit,
“ obfcuram finem habet.”

Cotunnius, de Aquod. Auris Plum. 1761. § 25, “ Continuari tamen hos

“ nervorum dudlus cum canaliculis inter lameilas fpiralis laminae defcriptis (xiv.) j
“ perque hos ad intervallum zonae cochleae nervorum ramulos tranfire, etfi pro
“ fumma tenuitate rerum non videam infpexiffe, extra omne tamen dubium afleri
u poffe credo. Ultra de hoc nervo me nihil fcire, lincerus fateor.”

J. Fr. Meckel junior. 1777. § :-:xiii. p. 40. “ Aperto enim cochleae tubo

“ a foramine rotundo ad ufque tertium iplius gyrum, ita ut, fupra et infra fep-
“ +um utraque fcala periofteo induta luftrari potuerit, etiam vitrorum, objedla,
u multum augentium, minifterio, nil intueri licuit, nifi albas inter trabeculas Co-
11 chleae ftrias.”

Martin, de Nervis. 1781. S. 2. p. 82. “ Vafculum aliquod fanguiferum
u pro nervo habitum eft, vel etiam portiunculas membranarum filamentorum fimi-
“ litudinem retulerunt.”

Sabatier. 1781. T 3. p. 252. “ Mes obfervations n’ont pu me donner.

u des lunaieres fur un chofe auffi obfcure*”

i96 OF THE STRUCTURE OF THE HUMAN COCHLEA

InjeCted Bones foft and tranfparent, and, in doing fo, had
remarked, that, though the Bones were made very Tender,
the Membranes connected with them retained a confiderable
degree of Tenacity, it readily occurred to me, that by this
means I might be enabled to trace the whole progrefs of
the Portio Mollis.

Accordingly my fuccefs equalled my expectation 3 and
with a great deal of pains I detached the Os Petrofum, and
the whole External Oileous Shell of the Cochlea from its
Interior Membranes ; and then took out the Membranes,
with the Modiolus and Lamina Spiralis fufpended by the
Trunk of the Portio Mollis : So that, by proper diffeCtion,

I could trace and fee diitin&Iy, not only the Divifion of the
Portio Mollis into its Larger Branches, but the whole Pro-
grefs and Termination of thefe.

I found, That the Portio Mollis is compofed of Two
Blanches nearly equal in fize 3 one of which fupplies the
Veftible and Semicircular Canals, and the other the Cochlea.
See Nervous Syfiem, Tab. XXX. Fig. 1, 2, 3, 4, 5.

That each Branch confifls of a great Number of Small
Cords. See Nervous Syftem, Tab. XXXI. Fig. 1, 2, 3. A A.

That

OF THE STRUCTURE OF THE HUMAN COCHLEA. 197

That the Small Cords of both Branches pafs through dif-
ferent minute Holes into the Veflible and Cochlea, or, that
the Bottom of the Canal in the Backpart of the Os Petro-
fum, commonly called Meatus Auditorius Internus, is Cribri-
form. See Nervous Syftem, Table XXIX. Fig. 12. X Y Z
cc d e.

As the Qfleous Partitions which divide the Cochlea into
its Gyri, as well as the Lamina Spiralis which divides the
Gyri into Scalae, are conne&ed to the Circumference of the
Modiolus j we might expedt to find the Branches of the
Portio Mollis conduced, from the Modiolus, to the Mem-
branes lining the Cochlea, by means of thefe Partitions, or
between or along the outer-fides of the Two Offeous Plates
which compofe them, as well as between the Two Lamellte
which compofe the Lamina Spiralis, or along the outer-fides
of thefe j as we would fuppofe, that the Two Sides of each
Scala fliould have Nerves diftributed on them in the fame
manner.

Accordingly, on profecuting the Branches or Fibres of the
Portio Mollis with the utmoft attention, I find, that they,
pafs Outwards from the Cavity of the Modiolus, through-
innumerable minute Holes or Canals, which every where

C c perforate

s9S OF THE STRUCTURE OF THE HUMAN COCHLEA.

perforate it. Some Fibrils pafs between the Two Plates
which form the Septa that feparate the Gyri from each
other. A Hill greater number of Fibrils pafies through
Holes between the Two Plates which compofe the Root of
the Lamina Spiralis. But by far the greated number of the
Nervous Fibrils perforates the Sides of the Modiolus, between
the OJTeous Septa and the Lamina Spiralis. The Fibrils
which pafs through the Holes that are neared; to the Lami-
na Spiralis, run to the Membrane covering the Lamina Spi-
ralis i whilft thofe which are neared to the Septa, run, in
a contrary direction, to the Membranes covering the Septa.
We perceive, therefore, that the part of the Membrane
lining each Scala which is the mod didant from the Mo-
diolus, will be fupplied by the Terminations of thefe Two
Sets of Fibrils meeting. The Nervous Fibrils on the Sur-
face of the Lamina Spiralis, feem larger, and are more re-
gularly difpofed, than thofe that run on the Surface of the
Septa. Two Plates are found in the Outer Odeous Part of
the Lamina Spiralis, and the Space between them is filled
with Nervous Fibres, from which numerous minute Fibrils
idue between the Outer Edges of the Two Plates. There
are likewife minute Holes in the Sides of each of the Plates
which compofe the Lamina Spiralis j and there can be no

doubt

OF THE STRUCTURE OF THE HUMAN COCHLEA. 199

doubt that the Nerves between the Plates are connected
with thofe which run on their External Surface,

The laft Branches or Fibres of the Portio Mollis pafs
through the Cribriform Plate, in the Top of the Modiolus,
which is common to it and the Infundibulum, to fupply the
lad: Half-Gyrus and Cupola of the Cochlea. See Nervous
Syftem, Table XXXI. Fig. 1, 2, 3. and Table I III. of this
Work.

I next obferved, that the feveral Branches of the Portio
Mollis, in their whole courfe along the Lamina Spiralis,
formed an elegant and intricate Plexus, by innumerable
Joinings and Separations of their component Fibrils. See
Nervous Syftem, Tab. XXXI. Fig. 1, 2, 3, 4, and Tab. IIIL
Fig. 1, 2, 3.

At the Root or Ofteous Part of the Lamina Spiralis, the
Nerves are White and Opaque j but at the Flexible and
Membranous Parts they are Semipellucid*. See Nervous
Syftem, Tab. XXXI. Fig. 1, 2, 3, 4. and Tab. III.

This Change of Colour is like to that we obferve the Op-
tic Nerve undergoes on entering the Eyeball to form the

C c 2 Xetina.:.

200

OF THE STRUCTURE OF THE HUMAN COCHLEA.

Retina : and, in. both, the Change of Colour is not very

gradually made, but fuddenly.

On comparing the Semipellucid Outer-part of the Lamina
Spiralis with the Retina of the Eye, I obferved a remark-
able difference ; to-wit, that in the Retina the Texture
feems Pulpy and Uniform, without any fuch appearance of
Fibres and Network as we might exped to obferve from the
name Retina , which has been fo long and univerfally given
to it j whereas, in the Ear, Fibres and the Continuation of
an intricate Network can be feen diftindtly in the Semipel-
lucid Part of the Lamina Spiralis, and as far as to its Outer
Edge. See Nervous Syftem, Tab. XXXI. Fig. 4. E F G.
and Tab. IIII. Fig. 1, 2, 3.

I have, therefore, in my Ledures, long obferved, that the
term Retina was improper when applied to the Nerve fpread
out on the Bottom of the Eye, and had been given, not in
confequenee of accurate obfervation of the Strudure*, but
from a common favourite theory of Anatomifis, which fup-
pofes that the Brain and Nerves coniift of Fibres. In the
Ear, the term may be,' with great propriety, applied to de-
fcribe the Appearance of the Branches of the Portio Mollis
in their courfe on the Lamina Spiralis.

OF THE STRUCTURE OF THE HUMAN COCHLEA. 201

At the Outer-part of the Lamina Spiralis, the Nervous Fi-
bres and Network become much lefs evident and, upon
the Continuation of thefe Membranes, on the Inner-fides of
the Gyri of the Cochlea, the Nerves feem to terminate ha a
Semipellucid Pulpy Subftance, very like to the Retina of the
Eye.

SECT. V.

I would next obferve, that the Membrane on which the
Branches of the Portio Mollis terminate in the outer tranf-
parent part of the Lamina Spiralis and on the Inner-fides
of the Gyri of the Cochlea, is not the Periofieum of the
Lamina Spiralis or of the Gyri, as has been univerfally fiip-
pofed, but is as different from it as the Pleura is from the
Periofieum of the Ribs. It is thick, foft, demipellucid,
and but flightly conneded to the Inner-fides of the Gyri ;
and, tracing the Branches of the Portio Mollis, it is evident-
ly formed by them carrying with them their Pia Mater,
nearly, as the Retina is formed by the Optic Nerve. Be-
fides, after detaching it from the Inner-fides of the Gyri,
the Bone is fo far from appearing bare, that we fee Blood-

vefiels

202 OF THE STRUCTURE OF THE HUMAN COCHLEA.

vefTels running upon its Surface, fupported by Membrane,
which is indeed fo thin and tender that we cannot eafily
raife it by difle&ion, but we can fhew it as diftin&ly as tha
Periofteum which lines the Cavity of the Tympanum.

CHAP,

CHAP. III.

Of the Ear in Whales.

O OUNDj I formerly obferved is conveyed to the Bot-
tom of the Ears in Whales, . by the fame general Struc-
ture as in Man and Quadrupeds.

They are all provided with a Meatus Auditorius Externus,
the Orifice into which, in the Cete Delphinus, is extremely
fmall ; and it appears to me probable, that they poflefs the
power of fhutting it, and excluding the water, when they
plunge to a confiderable depth. In the Cete Balaena, (i. of
Linneus), the largefi: of the Whale kind, there is within

the

* In my Book on Fifties.

204

OF THE EAR IN WHALES.

the Meatus Auditorius a Hard Body, upwards of an Inch in
Length, fliaped like an Egg, and attached by its fmall end
to one fide of the Meatus } which undoubtedly ferves as a
Valve, to prevent the Water, when the Whale dives deep,
from over-diftending and rupturing the Membrane of the
Drum f .

Their Membrana Tympani is tied by a Chain of Bones to
the Bottom of the Tympanum ^ but in this Chain the Os
Orbicular e is wanting, at leaft it is fo in the Phyfeter ; and
the Malleus is more fixed in its place than in Man.

I found, that they have likewife an Euflachian Tube, or
Internal Meatus Auditorius t, and that Cells, much larger in
proportion than thofe of our Maftoid Procefs, communicate
with the Cavity of their Tympanum. See Tab. V. Fig. 5.
and Tab. XXXV. Fig. 5, 6. on Fifhes.

Their Cochlea and Semicircular Canals, I obferved, were
analogous to ours.

When

4 See, in Table VI. *, a Figure of this, of its Natural Size, taken from a
Preparation I received lately from Mr Clapertqn.

OF THE EAR IN WHALES.

20$

When I firft publiflied on the fubjed, I thought it unne-
ceffary to trace their Semicircular Canals with accuracy.
But finding, by Dr Camper’s Letter, that he, after having
diffeded various Species of the Whale, perfifled in denying
their exigence, I have refumed the fubjed with greater at-
tention : And, after finding that I had been under no mif~

take in defcribing Semicircular Canals, I afked Mr Fyfe to
bellow fome pains in tracing their whole Extent, firft in the
Delphinus Phocaena, and afterwards in the Delphinus Delphis,
and in the Cete Phyfeter Macrocephalus or Spermaceti Whale,
which laft Dr Camper had diffeded , and to draw accurate
Figures of them to which, and their Explanation, I refer
the Reader. See Tab. V. and Tab. VI.

On viewing thefe Figures, the Reader will obferve, that
the Cochlea in the Cete Phyfeter is much larger than in
Man, but that the Semicircular Canals are fmaller : And,

fo far as I have examined the Ear, I have found, that the
Semicircular Canals in Man, bear a larger proportion to the
Cochlea, than they do in the Quadruped or Whale.

D d

CHAP

^ . '

•I

1 : .

, ; ’ ,1 ■: r, ,

*•' ■

CHAP. IV.

Of the Ear in Cartilaginous Fifties.

T> EFORE I publiftied my Work on Fifties, I had exa-
mined this fubjed with great attention ; and have the
fatisfadion to find, on repeating my experiments, that my
obfervations were corred in every refped : So that the

defcriptions I am about to give, contain a repetition of what
I formerly publiftied, but illuftrated with more elegant Fi-
gures drawn by Mr Fyfe.

D d 2

I ftiall

208

OF THE EAR IN CARTILAGINOUS FISHES.

I fhall confine my defcriptions chiefly, and almofl entire-
ly, to the Skate Fiili

In the upper and back part of the Head of a Skate, and
in a large Fifh weighing 150 pounds, at the diftance nearly
of One Inch from the Articulation of the Head with the
Firft Vertebra of the Neck or Atlas, Two Orifices, capable
of admitting fmall-fized flocking- wires, at the diflance of
about an Inch and Quarter from each other, furrounded
with a firm membranous Ring, may be obferved. See
Tab. VII. Fig. 1, 2, 3. Letters a a a a. Thefe are the Be-
ginnings of the Meatus Auditorii Externi.

If the Finger be applied a little farther forwards and in-
wards than one of thefe Orifices, and PrefTure made with it,
a White Vifcid Matter will generally be fqueezed out at the
Orifice.

* See Tab. VII. in the Firft Figure of which the parts are reprefented as they
appear on difleftion. In Figures Second and Third, they are reprefented as they
appeared, in a Fifh weighing 150 pounds, after being ftretched with melted wax
icje&ed into them.

OF THE EAR IN CARTILAGINOUS FISHES.

2C§

If a Small Probe be introduced at the Orifice, and a Cut
made upon the Point of the Probe, we difcover a Winding
Canal, nearly two lines, or the flxth part of an inch, in Dia-
meter, which defcribes more than three-fourths of a Circle.
See the fame Figures, Letters b b b b. This Winding Canal
may be compared to the Concha of our External Ear,

From the Concha, a Straight Paflage, capable of admitting
a finall ftocking-wire, leads outwards and downwards, (See
in the fame Figures the Letters c c c ), to terminate in a
Large Sac d d d d which we may compare to the Veffible
in the Human Body ; and which, in the Skate, contains a
very vifcid pellucid Humour, like the glaire of an egg, and
likewife a foft cretaceous Subxlance,

On the anterior part of the Large Sac, there is a much
Smaller Sac e e e e, containing fimilar Matter, and communi-
cating freely with the Large Sac at the Letters ////; and
at the pofterior part, there is a third very Small Bag, like-
wife containing cretaceous Matter, projecting from and com-
municating with the Large Bag,

We next find Three Semicircular, or rather Circular, Mem-
branous Canals, In each of them, there is a Bulb or dila-
ted 1

210

OF THE EAR IN CARTILAGINOUS FISHES.

ted part. All of them are inclofed within Cartilaginous
Canals, lined with Perichondrium, which are confiderably
larger than the Membranous Canals. The Membranous
Canals are filled with vifcid pellucid Humour, like to that
which is within the Veftible ; and a Fluid refembling this,
is lodged between the Perichondrium and the Membranous
Canals ; and thefe are tied to each other by Cellular
Threads, on which Arteries, correfponding Veins, Lympha-
tics, and very minute Nerves, are difperfed. See Table
XXXVII. Fig. 4. of my Work on Filhes.

One of thefe Canals is Anterior, See Tab. VII. Fig. 1, 2, 3.
Letters h i k l 0 $ and the part k is almoft over the part 0 ,
or this Canal may be called Anterior Perpendicular : At l

its Bulb is found. The Second or Middle Canal m n , is
placed almoft horizontally ; and its Bulb is feen at ?i.

The Anterior and Horizontal Canals join together, and
the wide Canal i h 0 is common to them. This Canal,
common to the Anterior and Horizontal Canals, commu-
nicates with the Small Sac e, by means of the Membranous
Tube g.

The

OF THE EAR IN CARTILAGINOUS FISHES.

2,11

The Third Circular Canal is Pofterior, and one half of ft
is over the other ; fo that it may be called Pofterior Per-
pendicular Canal. See q r f. Its Bulb is at J\ This Ca-
nal communicates with the Large Sac or Veftible, by means
of the Ducft p ; but has no direcft communication with either
of the other two Circular Canals.

Upon the whole, then,— The Meatus Auditorius Externus
leads to the Cavity of the Veftible. From this there is a
Paflage into a Smaller Sac, and, at the fame place, a Ducft
leads into the Membranous Canal which is common to the
Anterior and Horizontal Canals. From the Pofterior Part
of the Veftible, a Canal makes a Communication between the
Veftible and the Pofterior Canal. But the Anterior and the
Horizontal Canal have no direcft Communication with the
Pofterior Canal.

It appears, then, that from the Meatus Auditorius there is
a Paflage into the Large Sac or Veftible ; and that from
the Forepart of the Veftible, there is a Paflage into the
Small Sac, and, at the fame place, into the Canal which is
common to the Anterior and Florizontal Canals ; and that,
from the Backpart of the Large Sac or Veftible, there is a

Paflage

212

OF THE EAR IN CARTILAGINOUS FISHES.

PafTage into the Pofterior Canal ; and, hence, that all parts
of the Veftible and Circular Canals may be diredly affeded,
in the living animal, or, after death, may be injeded, through
the Meatus Auditorius Externus.

CHAP.

CHAP. V.

Summary of the Chief Circumftances above
defcribech

S feveral of the principal Fadts I have defcribed, have,

mofi unaccountably, been called in queftion, by Dr
Camper and Profeflbr Scarpa, I find myfelf under the dif-
agreeal-le neceflity of enumerating, in a fummary way, the
Chief Points, refpe&ing the Organ of Hearing in Man and
other Animals, in which, I apprehend, I have added to the
former flock of knowledge } and of then fubjoining the At-
teftation of the Royal Society of Edinburgh concerning

them,

E e.

Ac In

414 SUMMARY OF THE CHIEF CIRCUMSTANCES

A. In the Human Body, I have {hewed, That the Nerves
of the Veftible and Semicircular Canals, as well as thofe of
the Cochlea, pafs through numerous Small Holes or Cribri-
form Plates of the Os Petrofum

B. That all the Branches of the Portio Mollis which fup-
ply the Cochlea, pafs through innumerable Small Holes of
a Thin Conical Cribriform Plate which forms the Modio-
lus f.

C. That minute Nerves pafs through the Axis of the
Modiolus, to perforate that part of the Cribriform Plate
which Js common to it and to the Infundibulum, to fupply
the Infundibulum and that part of the Cochlea which it in-
cludes

D. That

* See Nervous Syftem, Tab. XXIX,
f See Nervous Syftem, Tab. XXIX.

+ See Nervous Sjftem? Tab. XXXL

ABOVE DESCRIBED.

a*5

D. That Branches of the Portio Mollis pafs along and be-
tween the Lamellae of the Qfleous Septa which divide the
Cochlea into its Gyri * ; or, that all of them are not con-
ducted by the Lamina Spiralis, as Scarpa has defcribed and
delineated f .

E. That the Nerves, in their whole courfe, particularly
along the Lamina Spiralis, join and again are feparated, fo
as to form a molt elegant Plexus in which new Combina-
tions of the Nerves are formed j:.

F. That the Nerves terminate on the Inner- tides of the.
Ofleous Gyri, in a demipellucid foft pulpy Membrane, re-
fembling the Retina of the Eye |j.

E e 2 G. That

* See Nervous Syftem, Tab. XXXI. and, of this Treatife, Tab. I1II.
f Scarpa, P. 55. and Tab. VIII.
t See Nervous Syftem, Tab, XXXI.

|| See Nervous Syftem, Tab. XXXI. and, of this Treatife, Tab. IIL

■2i6

SUMMARY OF THE CHIEF CIRCUMSTANCES

G. That this foft pulpy Membrane is not the Periofteum
of the Cochlea ; but as different from it, as the Pleura is
from the Periofteum of the Ribs.

H. In Whales, I have found an Euftachian Tube, which

had not been defcribed by Authors : I have ftiewn, that

Semicircular Canals are not wanting, as was affirmed by Dr
Camper ; and, in the Porpoife, I obferved, that the Mem-
branous Subftance, within the Gyri of the Cochlea, on which
the Portio Mollis is diftributed, might be feparated from the
Periofteum of the Cochlea ftill more eafily than in Man

I. In the Tortoife, as an example of the Amphibia, I

have defcribed the Euftachian Tubes, and the Connexion of
the feveral parts of the Ear, more accurately than had been
done by former Authors f : 'And it may be worth while to

add, that the Toad, as well as the Frog, is provided with
an Euftachian Tube, as this is denied by Geoffroy

K. In

* See Book on Fifties, Tab. XXXV. and, of this Treatife, Tab. V.
f See Book on Fifhes, Tab. XXXVI.

| Geoffroy fur 1’Organe de 1'Oul'e, 1778, p. 65,— 71.

ABOVE DESCRIBED,

217

K. In Tome of the Pifces of Linnaeus, I have not only
defcribed and painted the Connexion of the Semicircular
Canals, and of Sacs which may be compared to our Veftible ;
but I have traced, with accuracy, the Courfe and Termina-
tion of their Nerves *.

L. In the Skate and Angel Fifli, I have difcovered the
Orifices of the Meatus Auditorii ; fhewn the Winding of
their Conchae Aurium 5 the Terminations of their Meatus
Auditorii in the Veftibles ; the Communications of their Se-
micircular Canals with each other and with the Veftibles 5
and Diftribution of their Auditory Nerves, and of the Cir-
culating and Lymphatic VefTels of their Ears f.

M. Particularly, I proved, that the Semicircular Ca-
nals in Fifties were much fmaller than the Oneous or
Cartilaginous Tubes which inclofed them $ and that, fo
far from their being compofed of the Periofteum or Peri-
chondrium of thefe Canals, there was a conftderable Space

between

* See Book on Fillies, Tab, XXXIX,

f See Book on Fifties, Tab, VII, XXXVII- XXXVIIL and, of this Treatife,
Tab. VI. VII.

21 8 SUMMARY OF THE CHIEF CIRCUMSTANCES, &c.

between them, and the Periofteum or Perichondrium, filled
with Fluid, contained in a Cellular Subftance, on which mi-
nute Nerves, with numerous Circulating and Abforbing Vef-

fels, were difperfed, and conducted to the Perichondrium and

Periofteum I obferved farther, That in certain Fifties,
of the genus Gadus, Spheroidal Bodies, which I had difco-
vered, making in them part of the Nervous Syftem, were
difperfed in the Cellular Subftance, between the Semicircular
Canals and the Periofteum of the Tubes which contain,
them f.

CHAP,

* See Book on Fifties, Tab. XXXVII. XXXVIII. XXXIX,

•f See Book on Fifties, Tab. XXXIX,

CHAP

Atteftation as to the Fafts above defcribed,

TTAVING fully defcribed, and illuftrated by Tables, the
-*■ Chief Parts of the Ear in the different Clafles of Ani-
mals ; and having enumerated the particular Circumflances
I have difcovered which were unknown to former Writers m?
I fhall now add the Atteftation of the Royal Society of
Edinburgh refpeding fuch fads as have been called in que-
ftion by Dr Camper and Profeftbr Scarpa.

220

ATTESTATION AS TO THE FACTS

At their Meeting, in May 1794, I prefented to the Society
the following Letter :

“ Gentlemen,

“ AS one purpofe of your Society is to afcertain fuch
“ Fa&s as are defcribed by your Members or Correfpondents,
“ I take this liberty to requeft of you to appoint a Commit-
“ tee, confiding of thofe Members whom you may fuppofe to
“ be the mod: competent Judges of Anatomical Matters, to
“ examine certain Subje&s of which I propofe to give, foon,
u fome account to the Society, illudrated with Figures.

u I am,

u Gentlemen,.

“ Your mod; obedient Servant,

Edinburgh, ~6
May 2. 1794. _f

“ Alexr. Monro.

“ To the President and Other Members of the Royal
u Society.”

ABOVE DESCRIBED.

221

They accordingly appointed a large Committee of their
number, with a general invitation to any others of their
Members who might cjioofe to be prefent.

In confequence of this, the following Gentlemen met, on
the 9th of July 1794, in the Anatomical Theatre, at Mid-
day, that they might have the advantage of examining my
Dilfe&ions and Preparations with a clear light :

Profeflbrs of Medicine.

Mr John Robison, Profeflor of Natural Philofophy.

Mr Dugald Stewart, Profeflor of Moral Philofophy,
Mr Playfair, Profeflor of Mathematics.

Dr Black,

Dr Francis Home,

Dr Rutherford,

Dr Gregory,

Dr Duncan,

Dr Rqtheram, Phylician.

Dr Wright, Phylician.

Dr Charles Stuart, Phylician,

Dr Thomas Spens, Phylician.

Mr J ames- Russel* Surgeon.

F f

Along

22 2

ATTESTATION AS TO THE FACTS

Along with each of the Figures which I now publifh, I
demonftrated the Preparation from which it was delineated :
And it is to be obferved, that, in the Cartilaginous Fifties,
I had inje&ed, from the Orifice of their Meatus Auditorius
Externus, not only Air and Quickfilver, but melted coloured
Wax, into their Vefiible and Semicircular Canals; and that
I have about twenty fuch Preparations in my pofleflion.

The Committee, after having attentively examined thefe,
hereby declare, That the Tables and Preparations correfpond
exactly ; and that they faw diftindlly, in the Preparations,
all that is reprefented in the Tables.

1795. May 14.

On the 14th day of May 1795, I made the following
Demonftration to my Colleagues, Dr Home, Dr Gregory,
Dr Rutherford, and Dr Duncan.

In Two Large Skates, one the Raia Laevis, the other the
Raia Afpera or Thornback, I pointed out, with a Probe, the
Orifices of the Meatus Auditorii Externi.

I then

ABOVE DESCRIBED.

223

I then prefled with my finger on the Fore and Inner Sides

of thefe Orifices, and fhewed them, that a white vifcid Mat-

ter was difcharged from them.

A Sedtion was next made on the Right Side of both Fiflies,
and the Vefiible and Semicircular Canals of the Ear were
laid in view, without opening their Cavities.

A Small Iron Tube, fixed to a Large Glafs Tube, was

then introduced into the Orifice of the External Meatus Au-

ditorius, and Quickfilver was poured into the Glafs Tube.
The Quickfilver entered readily, and filled the Concha, and
ftretched the Skin over it fo that its Shape, Size, and
Winding, could be eafily difiinguiflied. From the Concha,
the Quickfilver palled readily into, and diftended, the Great
Sac, which contains the Cretaceous Matter.— The Paflage of
the Quickfilver from the Meatus Externus Auditorius into
the Sac or Vefiible, was feen diftimfily ; becaufe the Mea-
tus terminates in that part of the Vefiible which contains
the clear vifcid Matter, which is lodged between the upper
and outer or pofterior part of the Sac of the Vefiible and
the Cretaceous Matter.

Ff 2

Thev

224

ATTESTATION AS TO THE FACTS, &c.

They again examined the feveral Preparations in which
the Concha, Meatus Auditorius, Veftible and Semicircular
Canals, are filled with Wax of different colours in order to
Ihew the Communication of thefe Parts, and they compared
the Tables with the Preparations.

CHAP.

CHAR VII.

Remarks on Profeffor Scarpa’s Book on
the Ear*

T^IEFORE concluding, I find myfelf under the difagreeable
neceffity of pointing out the Injuftice of certain Criti-
cifms of Profellor ScaPvP a, and of enumerating the many un-
accountable Overfights and Errors he has committed ; and
I fhall quote the exprefllons he has thought himfelf at liber-
ty to employ.

SECT,

326 REMARKS ON PROFESSOR SCARPA’s

SECT. I.

In his Preface, p. 3. 1. 25. he has aflerted : “ Nam

quidquid nuperrime Monrous docuit de Acuftici Nervi
“ Diftributione per Laminam Cochleae Spiralem, nihil aliud
“ ell praeter mirificse fabricae fpecimen ; nec qua ratione
u Auditorius Nervus ad Utrumque Scalarum Cochleae Gy rum
pertingat, nec quo abeat Nervus ille qui per Centrum et
e‘ Axin JModioli defcendit, Vir alioquin cl., nobis patefe-
“ cit.”

The Reader, however, will obferve, that I have not only
•every year, fince 1756, fhewed, in my Anatomical Courfes,
the Preparation from which the Figure I publifhed was de-
lineated ; but that it was particularly examined, before I
publifhed, by the following Gentlemen : Dr Smith, Reader

of Anatomy in Oxford 5 Dr Soemmering, Dr Meckel ju-
nior, Mr Luther, Dr Black,- Dr Hutton, Dr Ruther-
ford: (See my Book on the Nervous Syflem, p. 45.) : And

that I hill preferve the Preparation and, on examining it
again, after reading the above aflertion, I find nothing ma-

% terially

BOOK ON THE EAR.

227

terially wrong in the Figure.- But, what is more diredly

in point, fo inconfiftent is Dr Scarpa, that, in the 55th page*
of his Work, where he defcribes the Pencils of Nerves pall-
ing from the Modiolus along the Lamina Spiralis, he quotes
my Book in the following words : “ Horum Penicillorum

“ fpecimen vide apud Monroum, Nerv. Syft.” And if the
Reader will take the trouble of comparing the Figures I
publidied, (See Nervous Syftem, Tab. XXXI. Fig. 1, 2,
3, 4.), with ProfefTor Scarpa’s Figures, (Nat. Difq. Tab. VII,
Fig. 1, 2.), he will find, that they correfpond fo much, in.
every general and material refped, that His Figure feemS'
little more than the Tranfcript of mine. They differ chief-
ly in the way in which the Nerves are prefented to view.
In my Preparation, I took off, with great pains, the whole
Outer Ofleous Shell of the Cochlea, and then lifted out the
Modiolus and Lamina Spiralis, fufpended by the Portio Mol-
lis ; fo that the whole Diftribution of the Nerve on the.
Lamina Spiralis is feen : Whereas Profefibr Scarpa has cut

open one fide only of the Cochlea.

I will farther venture to a fie rtf' that although Profeffon
Scarpa’s Figures are more ihewy and elegant than my firft

Figures-

228 REMARKS ON PROFESSOR SCARPA’s

Figures were, yet mine give a more diftind and accurate
Reprefentation of Nature.

He next alleges, That I had not fhewn how the Nerves
go to the Gyri of the Cochlea, as if he had fhewn this bet-
ter than I had done. But let the Reader compare our Fi-
gures ; he will find, that Profeffor Scarpa does not paint
the Nerves fo far as I had done in my Book on the Nervous
Syflem. I painted them as far as diftind Branches could
be feen with a Microfcope which magnified the objed to
thirty diameters. My defcriptions, when I publifhed on the
Nervous Syftem, were indeed very concife ; becaufe I had
the intention of profecuting the fubjed ft ill more fully than
I had then done.

In the next place, it is to be remarked, that One-half of
the Nerves the Scalae of the Cochlea receive, has efcaped
the obfervation of Profeffor Scarpa *9 to wit, All thofe which
run along the Offeous Septa to fupply the Outer-part of each
Scala, or that Part of each Scala which is mo ft diftant from
the Lamina Spiralis,

But

* See Scarpa, Cap. III. Be Nervo Auditorio, § viii.—xu. p. 54, 55, S6-

BOOK ON THE EAR.

229

But I mufl farther obferve, that Profeflor Scarpa, who
defcribes the Portio Mollis as terminating in the Periodeum
of the Cochlea, has neither attended properly to the Analo-
gy of the Optic Nerves, nor to the Strudure of the Mem-
branes within the Cochlea } for, from the defcription and
reafons I have given, it is evident, that the Periofleum, and
the Pulpy Membrane in which the Portio Mollis of the Co-
chlea terminates, are Diftind Membranes, the former having
the Common Strudure, and the latter refembling the Retina
of the Eye.

SECT. II.

In my Book on Fillies, p. 49. I obferved, That in each of
the Membranous Semicircular Canals, both in the Odeous and
in the Cartilaginous Fillies, there is a Dilatation or Pouch :
and, That the Membranous Canals are fo much fmaller, than
the Canals of Cartilage or Bone which contain them 5 that,
between them and the Cartilage or Bone, there is a vifcid
watery Liquor, contained in a Cellular Subflance, on the
Threads of which, Circulating and Abforbent Velfels, and
Nerves, are difperfed. (£.) See Tab. XXXVXL

G g

I likewife,

230 REMARKS ON PROFESSOR SCARPA’s

I likewife, after defcribing the Size and Courfe of the
Nerves, obferved, in treating of the Cartilaginous Fifhes,
That “ the Nerves, after reaching 'the Sacs and Canals, and
“ running a little way upon their Membranes, lofe their
il White Colour, become Pellucid, and difappear.” In
Tab. XXXVII. thefe Nerves are delineated from very large
Fifhes. And, fpeaking of the OITeous Fifhes, p. 51. I ob-
ferved, That “ very large Nerves are fixed to the Bulbous
“ Parts of the Semicircular Canals, and, fpreading out on
“ thefe Canals, they become fuddenly Pellucid.” See
Tab. XXXIX.

Still, however, other purfuits diverted me from the inten-
tion I had long had, of tracing the whole Diftribution jof
the Portio Mollis in the Human Ear.

In 1789, that is, four years after my Book on Fifhes ap-
peared, Profeflor Scarpa publifhed his Defcription of the
Membranes and Nerves of the Human Semicircular Canals :
And, although it is evident, as he does not appear to have
known any thing of the matter when he publifhed his “ Ob-
“ fervationes de Feneftra Rotunda et Tympano Secundario”
in 1772, and as he had then read my Works on the Ner-
vous Syftem and on Fifties, that he was led by the firft: of

thefe

BOOK ON THE EAR.

23 r

thefe to examine the Nerves of the Cochlea, and, on the
fuppolition of analogy, to examine the Veftible and Semicir-
cular Canals in Man ; yet, inftead of acknowledging this,
he tries to infinuate, that I had not traced the Nerves of
the Semicircular Canals in Fillies to their proper places, in
order to give the appearance of originality to his own de-
scriptions. Yet, after joining me with Mr John Hunter
as the author of an aflertion which Mr Hunter alone made,

3* ' ;

— where he fays, (in a note, p. 15.) “ J. Hunterus et Mon-
“ rous alferuerunt Canales Pifcium Semicirculares, Nervos
“ intus non fufcipere f’ adding, “ Qua Super re vereor quam
“ maxime Viros cl. examinafte tantummodo Cylindros, non
{( quidem Ampullas limul Canalium Seinicircularium in Pifci-
e( bus,” — he, in the fame note, refutes the truth of his alle-
gation, by Subjoining the following quotation from my Book :
“ Et Mqnrous, loc. cit. “ After reaching the Sacs and Ca-
“ nals, and running a little way upon their Membranes,
“ they loSe their white colour, become pellucid, and difap-
“ pear.” And with this description of mine, that of Pro-
feflor Scarpa exadly coincides : (See his Work, p. 34.

§ vi. L 7. ) : “ Neque enim in Homine, profpero magis Suc-

ceftu quam in PiScibus, Reptilibus, et Avibus, quantacun-
que adhibita diligentia, datum nobis fuit earn Pulpam, ul-

G g 2 « tra

232 REMARKS ON PROFESSOR SCARPA’s

“ tra Ampullaram fines, per continuos femicirculares Ductus
“ membranaceos, propagatara videre.”

In Tab. VIII. Fig. i, 2, 3. the Reader will find a more
exadt Reprefentation of the Divifion of the Acouftic Nerve
upon the Ampulla than Profeflor Scarpa could have given,
as it can be feen in very Large Fifties only ; which the
rude and inaccurate Figure he has publifhed, fhews he had
not examined.

SECT. III.

Professor Scarpa, difiatisfied with the account I had gi-
ven of the Structure of the Ear in the Cartilaginous Fifties,
undertakes one more accurate, and has exprefied himfelf in
the following terms. His criticifins are ftrangely disjoined,
and unnecefiarily repeated but I fhall endeavour to arrange
them fo as to render them as intelligible as pofiible.

Praef.

BOOK ON THE EAR,

2'3’3

Praef. p. 2. “ Has ob caufas Organ! Auditus Cartilagi-

“ neorum Pifcium pleniorem, quam adhuc fadum eft, de~
u fcriptionem tradere fufcepimus.”

Praef. p. 1. “ Monrous Externum hoc Auditus Odium

“ (Rajae) defcripferit, fufiiis atque delineaverit

“ Monroum vehementer fuper hac re hallucinatum fuifle.

“ Etenim nullum prorfus adeft OJlium Auditus extus

“ Adapertum in Cartilagineis Pifcibus, ejusque loco, fub Af-
“ pero horum Animantium Tegumento, Fenejira Ovalis repe-
“ riunda eft, Membranaceo Operculoy a nemine adhuc memo-
u rato, obduda.”

P. 8. § iii. “ In Cartilagineis Pifcibus nullum prorfas adeft
“ Oftium Auditus extus Adapertum, ejusque praenunciati Ojlii
u loco, fub communibus tegumentis, Fenejlram Ovalem , Operculo
u Membranaceo claufam, oftendimus,” &c.

P. 9. § v. “ Igitur in Summitate Capitis Rajae pone Oc~
u ciput, qua nempe cum Prima Colli Vertebra Colli neditur,

“ ablato Spinofo Tegumento, Sinuoiitas occurrit, in

“ qua Membranulae Duae, ovalis figurae Tympani ad modum.
u tenfae, confpiciendae funt. ......

?„9,

234 REMARKS ON PROFESSOR SCARPA’s

P. 9. § v. in a note at the foot of the page. “ Monrous,
u in Opere cui titulus “ Phyftology of Fifties,” Sed. III.
“ Tab. VII. Fig. 1, 2. docet in Raja, prope Junduram Capi-
“ tis cum Spina, adefle Foramina duo exigua, quae ad Aures
tl ducunt. Qua in re vehementer fibi hallucinatus eft Oftia
*l nimirum Duduum Mucoforum, ut manifeftum eft, pro Au-
“ ris Meatibus accipiens. Etenim omnino nullum eft in
“ Cartilagineis Pifcibus Oftium Auditus extus Adapertum,
li Membranaque Feneftrae Ovalis fub Communi Tegumento
“ recondita jacet et cooperta.”

P. 9. § vi. Note ( d.). “ Minime tamen ducit intra Ca-

i( yitates Sacculorum Veftibuli, quemadmodum Monroo vi-
“ fum eft ; cujus dodrina, ft vera eflet, ftmulque adeflent
il Oftia Auditus Externa, neceftario confequeretur liberum ef-
“ fe in Cartilagineis Pifcibus Aeri et Aquae Acceftum ad fe-
“ dem Organi Auditus immediati, ipfamque Pulpam Nervi
“ Auditorii 5 quod et abfurdum eft, et a rei veritate quam
“ maxime alienum!”

Praef. p. 2. a Praeterea, Monro us nefcio quam Organi
u Auditus Cartilagineorum Pifcium hiftoriam confcripfit, ut,
M nift vehementer fallimur, ex ipfius fententia deducere uni-

“ cuique

235

BOOK ON THE EAR.

“ cuique liceat in Pifcibus Cartilagineis Meatum Auditus Ex-
“ ternum ducere intra Saccuios Capillorum, atque ab his ad
“ Canales Semicirculares, Nervumque Auditorium ; proin,
“ Aquis admixtisque heterogeneis particulis nullatenus in
“ Cartilagineis Pifcibus impeditam yiam efle ab Externo (ut
“ ait) Auris Meatu, ad immediatam Auditus fedem ; quae res
“ profedo a veritate et perfpeda Naturae provident! a qusUn
“ longillime diftat !”

P. 12. § xv. a Interim praeftabit monere, Canales Semi-
<e circulares Membranofos, quamvis pluribus in fedibus La-
pillorum Sacculis alligati funt, nullibi tamen cum iifdem
“ Sacculis communicare \ quod iteratis periculis, modd
“ Aerem, fervata naturali fede, per Canales Semicirculares
“ Membranofos infufflando, modd Hydrargyrum injiciendo,
“ cognovimus.” — Note (e. J. a Minime ignoramus Mon-
“ roum in Raja defcripfiffe ac delinealfe.”

From the above quotations, then, it appears, that Profeffor
Scarpa, even after having read and Rudied the Defcription
and Figures I had given of the Strudure of the Ear in the
Skate, illuftrated by a number of Tables, had not been able
to difcover the External Mouth, or Ostium, of the Meatus

Auditorius 5

236 REMARKS ON PROFESSOR SCARPA’s

Auditorius ; the Concha Auris ; the Continuation of the
Meatus Auditorius ; the Termination of it in the Vedible,
or Large Sac, containing vifcid and cretaceous matter ; the
Communication of the Large Sac, or Vedible, with the
Smaller Sac, nor the Communication of the Semicircular Ca-
nals with thefe Sacs or Veftibles. Yet, in my experiments,
not only Air and Quicklilver readily palled in all dire&ions ;
but, in a great number of Preparations in my polfellion, all
the PalTages and Communications I defcribed in my former
Work, are filled with melted and coloured Wax, and were
didin&ly feen by every Member of the Committee of the
Royal Society of this place, and by many Students who have
examined them.

One thing only, which might be apt to dagger fuch as
have not had the opportunity of feeing my Preparations, re-
mains to be explained ; I mean what relates to a Fenejlra
Ovalis, which is mentioned by Profeflor Scarpa, “ Membra-
il naceo Operculo obdu&a, a nemine adhuc memorata.”

If the Reader will compare my Book on Filhes, Tab.
XXXVII. Fig. 2. with Profelfor Scarpa’s, Tab. I. Fig. i.
e e , he may obferve this Fenedra delineated by me, and a

large

BOOK ON THE EAR.

-37

large pin ftuck through it, with the following explanation,
page 1 15. 1. 22. “ Behind the Concha, there is a Large Soft
“ Part, which is fliewn by a pin ftuck through it.” I did
not call it Feneftra Ovalis $ becaufe, as I had difcovered a

Meatus Auditorius Externus leading into the Cavity of the

Veftible, I was certain it had no analogy to our Fenefcra
Ovalis : And Dr Scarpa, though ignorant of the exigence

of the Meatus Externus, might have perceived that it did
not referable the Structure of the Tortoife, to which he com-
pares it, (in p. 16. § xxvii. 1. 23.) ; for, as he immediately
afterwards obferves, (1. 27.) “ I11 Cartilagineis Pifcibus mox
“ retro Membranam Feneftrte Ovalis omiftt Natura Officulum,
“ quod in Reptilibus plerifque altera extremitate Tympano
“ nexum eft, altera, ftapedis ad modum, Feneftram Ovalem
“ obftruit.”

In Table VI. Fig. 2, 3, 4. T. I have given a ftill more
exact Reprefentation of this Soft Part.

I then fuppofed, and ftill do fuppofe, that Nature has
formed one part of the Cafe which contains the Veftible and
Semicircular Canals, Soft and Flexible, in order that, by its
yielding, the Parts within might be fufceptible of Tremulous

PI h Motion-

23'3 REMARKS ON PROFESSOR SCARPA’s

Motion when Sound ads upon them through the Meatus Au-

ditorius Externus.

After eftabiifhing the fad, that the Skate and Squalus
Squatina are provided with a Meatus Auditorius Externus, it
mull feem very fuperfluoiis to the Reader to take any notice
of what ProfejTor Scarpa has Rated about the danger of
Water and Heterogeneous Matter getting into the Veftible
and Semicircular Canals, injuring the Auditory Nerve, &c. :
Yet, I cannot help obferving, that Profellbr Scarpa feems to
have forgotten, not only that the Orifice of the Meatus is
like that of the Whale ; but likewife, that, from the Obli-
quity of the Meatus or Concha under the Skin, there is no
more danger of Air, Water, Sand, &c. getting into the Ear,
than there is, that the Drink, the Chyle, or the Urine, fhall
get into the Salivary or Biliary Duds or Ureters ; and like-
wife, that thefe Parts are quite full of Vifcid Matter in-
elofed in Membranes, incafed in Thick Cartilages, which
therefore will refift the entrance of external Fluids or
Solids*

Were

BOOK ON THE EAR.

239

Were it worth while, I might obferve farther to him,
That I have, in the very fame Animal, difcovered and de-
fcribed two much larger Palfages, with open Orifices, by
which the Cavity of the Abdomen communicates with the
Water of the Ocean ; and, again, within the Animal,
Tubes by which the Cavity of the Pericardium communi-
cates with the Cavity of the Abdomen ; yet the Interior
Parts fuffer no Injury

H h 2

EX-

TAB. 1.

ZX 3-

EXPLANATION

OF THE

TABLES.

Explanation of Table I.

THE Figures in this Table give an accurate Reprefenta-
tion of Metal, with which the Cavities of the Human Ear,
on the Right Side of the Body, had been filled.

FIG. i, 2.

Fig. i. reprefents the Forepart of the Metal, and Fig. 2. the
Backpart of it.

a Reprefents

EXPLANATION OF TABLE I.

Reprefents the Metal which filled the Ofleous Part
of the Meatus Auditorius Externus.

The Ring where the Membrana Tympani was con-
ne&ed.

The Cavity of the Tympanum filled.

The Root of the Cells of the Maftoid Procefs where
they communicate with the Cavity of the Tym-
panum.

The Metal which filled the Cells of the . Maftoid
Procefs.

(Fig. i.) The Canal filled which contained the Ten-
for Membrana Tympani.

The Outer Ofleous End of the Euftachian Tube
filled.

The Veftible filled

EXPLANATION OF TABLE L

i The Cochlea completely filled,

k The Root of the Scala Tympani of the Cochlea,

l The Root of its Scala Veftibulh

m (Fig. i.) The Forepart of the Beginning of the An-

terior Perpendicular Semicircular Canal filled,

n (Fig* i.) The Forepart of the Beginning of the Ho-

rizontal Semicircular Canal filled,

9 The Canal common to the Two Perpendicular Semi-

circular Canals filled.

p q (Fig. 2.) At the Places to which the dotted lines,
drawn from p and q, lead, the other Ends of the
Pofierior, Perpendicular, and Horizontal, Semicir-
cular Canals, are reprefented, filled with the Metal.

f i a

EXPLANATION OF TABLE L

FIG. 3, 4.

Fig. 3. fhews the Metal with which the Cochlea had been
filled, as it appears when we look into the Conical Cavity
M, which the Modiolus had occupied, and which was not
filled with the Metal.

Fig. 4. gives the fame view of the Preparation magnified to
Four Diameters.

a b c The Scala of the Tympanum filled.

d e Part of the Scala of the Veflibulum feen in this
view. The reft of it, is hid by the Scala of
the Tympanum.

Explanation

TAB- II.

Tyf. a

or 3.

. LA,/, AA

tS. ■ fr dill cue

EXPLANATION OF TABLE IL

-45

Explanation of Table IL

The Figures of this Table reprefent, in the Ape and dif-
ferent orders of Quadrupeds, remarkable Varieties of the
Size and Shape of the Cavity of the Tympanum ; and of
its Communication with a Cavern, or with Caverns, analo-
gous to thofe of our Maftoid Procefs*,

’F I G. i.

Reprefents the Under Part of the Bones of the Head in
the Ape.

A A Protuberance in the Under Part of the Left Os

Petroftrai.

B A fimilar Protuberance of the Right Os Petrofum

cut, to fhew a number of Cells, without Marrow,
which it contains, and which communicate with
the Cavity of the Tympanum.

G A Probe palfed from the Meatus Auditorius into the

Cavity of the Tympanum.

D A Probe palfed through the Euftachian Tube into

the Cavity of the Tympanum.

Thefe Protuberances, therefore, referable in office our
Maftoid Precedes, but are differently ft mated.

1 i Fig. 2,

246

EXPLANATION OF TABLE II.

Fig. 2. reprefents fimilar Protuberances in the Tiger, and
Fig. 3. fuch Protuberances in the Sheep : But, on cutting

them, Large Caverns, communicating with the Cavity of the
Tympanum, are found, inftead of numerous minute Cells.

In the Dog and the Horfe thefe Protuberances agree fo
much, in lituation and ftru&ure, with thofe of the Tiger and
Sheep, that I thought it unneceflary to have the Drawings,
of them Engraved.

It may be worth while to obferve, that, in the Ape, thefe
Protuberances are fituated as in the Quadruped ; but, that
their cellular ftru&ure correfponds with that of the Human
Maftoid Procefles.

Explanation of Table III.

In this Table, the Ofteous Stru&ure of the Human Co-
chlea and Veftible is reprefented.

FIG. i.

This Figure ftiews, on the Left Side of the Body, the Paf-
fages for the Branches of the Portio Mollis into the Cochlea
and Veftible ; and the Cavity of the Veftible laid open, on
its Backpart, by cutting away a Portion of the Inner and
Pofterior Part of the Os Petrofum.

* The

. I

EXPLANATION OF TABLE III.

'247

* The Inner and Poderior Part of the Os Petrolum.

a The Bottom of |the Canal which contains the Left

Branches of the Auditory Nerves.

b The Canal of the Portio Dura of the 7th Pair.

c d A Cribriform Plate, through which the Branches of
the Portio Mollis pafs into the Cochlea.

e The Continuation of the fame Cribriform Plate, form-

ing the Centre and Bottom of the Cavity of the
Modiolus.

/ g Cribriform Plates, through which Branches of the
Portio Mollis pafs into the Vedible.

b h The Cavity of the Vedible laid open, by cutting
away the Bone which covers its Poderior Part.

i The Foramen Ovale.

k A Probe palled from the Veflible, into the Scala

Vellibuli of the Cochlea.

I The Anterior, and m the Poderior, End of the Su-

perior Semicircular Canal.

n The Upper, and 0 the Lower, End of the Poderior

Semicircular Canal.

p The Termination, in the Veflible, of the Tube which

is common to the Superior and Poderior Semicir-
cular Canals, or which is formed by the joining
together of their Ends m n.

q The Fore, and r the Poderior, End of the Exterior

Horizontal Semicircular Canal.

I i 2

F I G.

248

EXPLANATION OF TABLE III.

, .

F I G. 2.

Gives a View, from above, of the Cochlea, and Part of the
Veflible and Semicircular Canals, of the Right -Side, after
cutting away Part of the Os Petrofum.
a The Os Petrofum.

b The Canal for the Internal Carotid Artery.

c The Anterior End of the External Horizontal Semi-

circular Canal.

d The Anterior End of the Superior Semicircular

Canal.

e The Upper Part of the Veflible.

f The Side of the Cochlea viewed fomewhat obliquely.

g h i i The Outer Part of the Modiolus, which is Cribri-

form, or pierced with a number of Holes, for the
Pailage of the Branches of the Portio Mollis.
k A Wire palled between Two Plates or Lamellae, of

which the Modiolus confilts, and which are at the
greateft di fiance from each other, and therefore
belt feen at its Root.

} l The OlTeous Septum between the Firft and Second

Gyrus of the Cochlea, compofed of Two Tables
or Plates.

m The OlTeous Septum which feparates the Second Gy-

rus of the Cochlea from the Infundibulum.

■ ' • nop The

EXPLANATION OF TABLE III.

249

nop The Firffc Turn of the Ofleous Part or Root of the
Lamina Spiralis. At 0 it is cut, to fhew that it
conflfts of Two Tables, between which Branches
of the Portio Mollis are lodged, which, after di-
viding into very minute Filaments, pafs through,
innumerable Holes, which are delineated on the
Outer Edge of the OITeous Part of the Lamina
Spiralis.

q The Second Turn of the Ofleous Part of the Lamina

Spiralis.

r The Termination of the Lamina Spiralis in a Hamus

or Hamulus, the Concave Side of which is con-
nected with, or continued from, the Ofleous Sep-
tum my which divides the Second Gyrus from the
Infundibulum.

/ The Infundibulum, at the Bottom of which a CribrN

form Ofleous Plate is feen, between it and the.
Apex of the Modiolus, through which Nerves pafs.
from the Modiolus into the Infundibulum.
t u The Firfl: and Second Scala of the Tympanum.

v w The Firfl: and Second Scala of the Yeflible.

F I G. 3.

In this Figure, the Side of the Cochlea is turned a little
more outwards than in Fig. 2. by which the Outer Edge of
the Lamina Spiralis, and. Structure of the Ofleous Septum be-
tween the Scalae of the Cochlea, are better feen.

a Reprefents

25o EXPLANATION OF TABLE III.

a Reprefents the Bails of the Cochlea.

b The Root of the Cribriform Modiolus.

c The Root of the Lamina Spiralis, 'which is likewife

Cribriform.

d The Outer Edge of the OiTeous Part of the Lamina

Spiralis, where the Two Laminae which compofe it
are feen, with innumerable Holes for the Paffage
of the Branches of the Nerves which are placed
between the Laminae.

■s A Sedlion of the OiTeous Septum, which divides the

Firft from the Second Gyrus of the Cochlea, and
which conffffs of Two Laminae.

J The Scala Tympani, and g the Scala Veftibuli.

FIG. 4.

Reprefents the Cochlea, and a fmall part of the Semicircular
Canals, after cutting off from them the Fore and Outer Part
of the Os Petrofum.

a The Fore and Outer Side of the Os Petrofum.

b The Paffage for the Internal Carotid Artery.

c Part of the Veftible.

d The Anterior End of the External Horizontal Semi-

circular Canal.

e The Anterior End of the Superior Semicircular Canal.

f The Bails of the Cochlea.

g The Scala of the Tympanum.

b The

•( '

TAB. TV

EXPLANATION OF TABLE III.

2$t

h The Outer Edge of the Ofleous Part of the Lamina

Spiralis, in which there are innumerable Small
Holes for the Paflage of Nerves.
i A Ridge in the Middle of the Ofleous Part of the

Lamina Spiralis, where the Two Plates which com-
pofe it are at fuch di dance from each other as ta
produce a Riling or Ridge.

k k The Ofleous Septum which divides the Fird from the
Second Gyrus of the Cochlea.

/ The Scala of the Veflible.

m The Second Gyrus of the Cochlea.
n The Lamina Spiralis, terminating in a Hamus or

Hook.

o The Infundibulum.

Explanation of Table IV.

The Three Figures of this Table reprefent the Didribution
of the Branches of the Portio Mollis ^within the Two Scalae
of the Cochlea, or the Nervous Webs or Retinae thefe form.

FIG. i.

Reprefents the Didribution of the Branches of the Portio
Mollis, on one lide of the Lamina Spiralis.
a The Large Branches of the Portio Mollis, at the

Root or Ofleous Part of the Lamina Spiralis.

b The

EXPLANATION OF TABLE IV.

The Continuation of thefe Branches on the Soft Part
of the Lamina Spiralis.

The Outer Part of the Lamina Spiralis, feparated
from the Bone of the Cochlea.

Thefe Nerves, in their whole courfe, form an intri-
cate and beautiful Plexus, by repeatedly joining
into Trunks, and thefe feparating into Branches.

FIG. 2.

Reprefents the Modiolus.

The Plexus of Nerves on the OHeous Part of the
Lamina Spiralis.

The Plexus of Nerves on the Outer and Softer Part
of the Lamina Spiralis.

The Outer Part of the Lamina Spiralis, dividing into
its two conilituent Layers or Membranes, one of
which d , continued, lines the Scala of the Veflible,
and the other Layer e, continued, lines the Scala
of the Tympanum.

F I G. 3.

Reprefents the Modiolus.

The Plexus of Nerves on the Lamina Spiralis.

At c, the Layer of the Lamina Spiralis, the Conti-
nuation of which formed the Retina of the Scala
of the Tympanum, is cut off.

d Shews

■

. I

/C'lMJ, Jr.

TAB . V

AFy/' dtf-

EXPLANATION OF TABLE IV.

253

d Shews the Continuation of the other Layer of the
Lamina Spiralis lining the Scala of the Veftible,
c Is an Incifion, where the Retina of the Scala Vefti-

buli begins to be continued from the Lamina SpL
ralis.

Explanation of Table IV. #

This Table reprefents, of its Natural Size, a Portion of
the External Meatus Auditorius of the Cete Balaena, i« of
Linneus, laid open.

A The Outer and Wider End of the Meatus.

B The Inner and Narrower Part of it.

C A Smooth Spheroidal Body, the Inner End, or Root,
of which, D, is Smaller than its Outer End, and
is attached to the Side of the Meatus.

Explanation of Table V.

The Firft, Second, Third and Fourth Figures of this Table,
reprefent the Veftible, Semicircular Canals, and Cochlea, of
the Cete Delphinus Phocsena of Linneus, or of the com-
mon Porpoife.

The Diameter of all the Parts, which belonged to the
Right Ear, is magnified a little ; nearly, in proportion to
the real Diameter, as Three to Two.

K k

The

254

EXPLANATION OF TABLE V.

The Same Parts are pointed out by the Same Letters ia

all the Four Figures.

A The Outer-lide of the Os Petrofum.

B The Veftible laid open-

C The Foramen Rotundum.

D E (Fig- 3-) The Apex and Bails of the Cochlea opened.

F The Ends of a Wire twilled together, after palling

it, from the Foramen Rotundum, out at an Open-
ing made into the Scala Tympani of the Cochlea.

G The Ends of a Wire twilled together, after palling

it, from the Foramen Ovale, out at an Opening
made into the Scala Vellibuli of the Cochlea.

H The Ends of a Wire twilled together, after palling
one end of it, from a Hole in the Superior or An-
terior Semicircular Canal, into the VeRible, and,
from that, out at the Foramen Ovale.

I The Ends of a Wire twilled together, after palling

both ends of it, from the Cavity of the Pofterior
Semicircular Canal, into the Veliible, and then out
at the Foramen Ovale-

Thefe Two Wires are contiguous in the Canal com-
mon to the Two Perpendicular Semicircular Canals.

K A Short Wire put into one end of the Third or Ho-
rizontal Semicircular Canal.

L The Hole, on the Backpart of the Os Petrofum, for
the Pallage of the Portio Mollis, and Portio Dura
of the 7th Pair of Nerves.

M That

EXPLANATION OF TABLE V.

255

M That Branch of the Portio Mollis, which furnilhed
Nerves to the Cochlea, dried.

N The other Branch of the Portio Mollis dried, which
furnilhed Nerves to the Veftible and Semicircular
Canals.

FIG. 5.

This Figure reprefents the Os Petrofum and the Parts of

the Ear, of their Natural Size, in the Cete Phyfeter Macro-

cephalus of Linneus, or the Spermaceti Whale.

A A Part of the Os Petrofum, within which there is a
Large Cavity, that communicates with, or makes
part of, the Cavity of the Tympanum B B. This
is, in Stru&ure and Office, analogous to the Hu-
man Maftoid Procels, or to the Hollow Part of
the Os Temporum of the Ape and Quadrupeds re-
prefented in Table II.

C D E The Malleus, Incus, and Stapes, conne&ed to each
other by Ligaments. The Root of the Stapes fills
the Foramen Ovale.

F A Hole cut in the Bone* in order to ffiew the Ca-

vity of the Veftible.

G H Two of the Semicircular Canals, cut open to their
Terminations in the Vefiible.

I The Scala of the Cochlea which begins at the Fora-

men Rotundum, which is called Scala Tympani.

K A Probe in the Scala VeflibulL

Kk 2

L The

256

EXPLANATION OF TABLE V.

The Firft Gyrus of the Cochlea cut open, in which
the Ofieous Root of the Lamina Spiralis is obfer-
vable.

The Second Gyrus of the Cochlea.

The Hole which tranfmitted the Fordo Mollis of the
7th Pair of Nerves.

A Probe in the Winding Canal, which tranfmitted
the Portio Dura of the 7th Pair.

Explanation of Table VI,

In this Table, fome of the Principal Parts of the Ear in
the Cete Delphinus Delphis are reprefented.

FIG. 1.

Shews the Orifice of the Meatus Auditorius Externus.

A The Left Eye.

B The Corner of the Mouth.

C D White Lines or Streaks on the fide of the Head and
Body.

E A Brittle introduced into the Orifice of the Meatus
Auditorius Externus.

FIG. 2.

Reprefents the Meatus Auditorius Externus laid open, the
Euttachian Tube and Cavities refembling thofe in the Ma-

ftoid

O O

)

• /

«c

i •'

EXPLANATION OF TABLE VI,

*57

ftoid Procefs, with which this Tube and the Cavity of the
Tympanum communicate.

A The Eye.

B The Orifice of the Meatus Auditorius with a Bridle

introduced into it.

C The Meatus Auditorius laid open.

E E Probes introduced into the Euftachian Tubes.

F G The Outer End of the Tube opening into Large Cells.
H A Bone which is Hollow.

In FIG. 3.

F Reprefents the Outer End of the Euftachian Tube,,,
with a Probe pafled from it into Large Cells.

Another Probe pafled from the Outer End of the
Euftachian Tube into the Cavity of the Bone H,
the Lower Part of which is cut off, in order to
{hew its Cavity.

F I G. 4.

Shews the Portio Mollis terminating in the Cochlea and Se-
micircular Canal.

A B The Inner Sides of the Bafe of the Cranium.

C The Trunk of the Portio Mollis.

D The Os Petrofum.

E The Portio Mollis going into the Modiolus.

F G The Sides of the Cochlea laid open.

H One-

EXPLANATION OF TABLE VL

^5?

H One of the Semicircular Canals laid open,

I - The Portio Dura of the 7th Pair.

Explanation of Table VII.

The Figures in this Table reprefent the Situation and Con-
nexion of the feveral Canals of the Ear in a Skate Filh, of
their Natural Size.

FIG. 1.

In this Figure, the Situation of the Two Eyes, and of Two
Paflages which lead from the Upper Part of the Head into
the Throat, and of the feveral Parts of the Brain and Nerves
riling from it, are reprefented, along with the Parts of the
Ear.

AAA A Reprefents a Se&ion of the Skin and other Parts of
the Upper Side of the Head and Spine.

B B The Eyes.

C C Two Paflages leading down into the Throat.

D The Forepart of the Cavity of the Cranium, which

contains fome Cellular Subftance, and is filled with
a tranfparent vifcid fait Liquor.

E The Brain.

F The Cerebellum.

1 1 The Olfa&ory Nerves.

2 2 The Optic Nerves.

33 44 Nerves which refemble the 3d and 4th Pairs.

5 5 Nerves

■■

EXPLANATION OF TABLE VII.

259

5 5 Nerves which referable our 5th Pair, and likewife
the Molles of our 7th Pair.

G The Skin covering the Occiput.

H H The Joints of the Head with the Spine, or Joining
of the Condyles of the Occiput with the Firft
Vertebra or Atlas.

I The Skin covering the Spinal Procedes of the Verte-

brae.

KLM KLM Thick Cartilages, cut horizontally, which cover
and contain Three Semicircular, or rather Circular,
Canals of the Ear, and certain Sacs, analogous to
our Veftible, with which thefe communicate.

a a The Mouths or Openings of the Meatus Auditorii *
Ex.erni.

ah ah Winding Canals cut open, which refemble the Con-
chae of the Human Ears.

e A Bridle paffed from the Concha of the Left Exter-

nal Ear, into a draight Meatus Auditorius Exter-
nus, and, from it, into the Cavity of a Large Sac
d, refembling our Vedible, which is filled, partly
with a regularly-diaped white foft cretaceous Sub-
dance, and partly with a tranfparent vifcid Fluid,.

d In the Right Ear, reprefents the fame Sac.

e A Small Sac, lituated on the Forepart of the Large

Sac d, containing likewife a Cretaceous Subdance
and Vifcid Fluid,

* A.

*6o EXPLANATION OF TABLE VII.

* A ftill Smaller Sac, or rather a Projedion from the

Backpart of the Large Sac d, which alfo contains
Cretaceous Matter.

/ The Place at which the Large Sac d communicates
with the Small Sac e .

g A Tube leading from the Small Sac <?, to h, which

is a Canal common to the Anterior Perpendicular
Circular Canal i k /, and to the Middle Horizontal
Circular Canal i m n.

I Is a dilated Part or Bulb in the Anterior Circular

Canal, and n is a ftmilar Bulb in the Horizontal
Circular Canal.

i h o A Large Canal common to the Anterior and Hori-
zontal Middle Canal.

p q A Canal leading from the Inner and Pofterior Part
of the Great Sac d, to the Pofterior Perpendicular
Circular Canal q r f. At f there is a Bulb in this
Canal, and at its Inferior End q it is Wider than
it is in its Upper Part.

FIG. 2, 3, 4.

Much Larger Fifties than the former were procured for the
Preparations reprefented by thefe Three Figures ; and in the
Preparations reprefented by Fig. 2, 3. the Meatus Auditorius
Externus, Veftible, and the Circular Canals, were injeded

with

EXPLANATION OF TABLE VIL

261

. >

with melted Wax, tinged with three different colours, fuch
as thofe with which thefe Figures are painted.

In the Preparation reprefented by Fig. 2. the Veftible was
laid in view and delineated, before the inje&ion was thrown
in j and the Boundary of the Cretaceous Subftance is fcen
at the letter d.

After all the Canals were injeded, in the Preparation re-
prefented by Fig. 3. the Veftible was cut, and the Wax taken
out of it, that its Communications with the Meatus Audito-
rius Externus, the Small Anterior Sac, and the Canal which
leads to the Pofterior Circular Canal, might be more fully
feen and delineated.

The feveral Parts reprefented in thefe Three Figures are
pointed out by the fame letters as in Fig. 1. ; fo that the
Explanation already given of Fig. 1. beginning with the let-
ters K L M, applies to Figures 2, 3, 4.

The Meatus Auditorius Externus c paffes under the Termi-
nation of the Irmer-part of the Middle Horizontal Circular
Canal, in the Canal i h 0, common to it and to the Anterior
Circular Canal. ■

Behind the Meatus Auditorius Externus, the Pofterior Cir-
cular Canal is contiguous to the Horizontal Circular Canal,
but does not communicate diredly with it by any Opening.

In Fig. 3. at the letter T, the Outer-ftde of a large round
Hole or Aperture in the Cartilage which inclofes the Vefti-
ble and Circular Canals, is delineated 3 and, in Fig. 4. at T,

LI s the

26z

EXPLANATION OF TABLE VII.

the Inner-fide of this Hole is reprefented ; and, in Fig. a*
at the fame letter, the Place of the Skin is pointed out, un-
der which this Hole is fituated.

Explanation of Table VIII.

In this Table, the Nerves of the Veftible and Circular

Canals in the Right Ear of a Skate are reprefented, after in-
verting the Head, and cutting away the Cartilages which lie

under them.

ABCDE A Se&ion of the Cartilages.

F G The Right Side of the Medulla Oblongata.

HI A Nerve which, in its Diftribution, refembles the

Human 5th, and Portio Mollis of the 7th Pair.

IC A Branch of the Portio Mollis fent to the Bulb of
the Anterior Circular Canal.

L A Branch of it fent to the Bulb of the Middle Ho-
rizontal Circular Canal.

M A Branch of it fent to the Anterior Sac which com-
municates with the Veftible.

N A Number of Branches, forming an elegant Plexus

on the under Part of the Veftible.

O Branches fent to a Small Projection or Sac at the

Under and Pofterior Part of the Veftible.

P A Branch

TAB vm.

■ SL

//r.

EXPLANATION OF TABLE VIII.

263

P A Branch fent to the Bulb of the Poffcerior Circular
Canal.

Q. A Nerve refembling the Human Portio Dura of the
7th Pair.

S T Nerves refembling the Human 8th and 9th Pairs of
Nerves.

F I G. 2, 3.

Shew, more fully, the way in which the Branches of the
Portio Mollis terminate in the Bulbs of the Circular Canals.

a b The Cylindrical Parts of the Circular Canals.

c (Fig. 2.) Shews the Bulb entire ; and c, in Fig. 3.,

fhews the Bulb cut open, in order to bring into
view an imperfed Septum, e , on which the Nerve
fplits into a great number of minute Branches ;
which, in a very large Fifh, weighing upwards of
160 pounds, I have obferved to form a Plexus on
the Septum ; and, the Branches then becoming
pellucid, it is impoflible to perceive their farther
Diftribution on the Cylindrical Part of the Circu-
lar Canals.

THE END OF TREATISE THIRD.

k 4

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